These are a some books and web pages I have found useful in my research:

Print Sources:

The 1811 Dictionary of the Vulgar Tongue, Buckish Slang, University Wit, and Pickpocket Eloquence, Senate 1994.  (ISBN 1859580459)

Ackermann's Costume Plates, Women's Fashions in England, 1818-1838, Dover Publications, 1978. (ISBN 0486236900)

Jane Austen's Christmas, Maria Hubert, Sutton Publishing, 1996.  (ISBN 075091307X)

Jane Austen's England, Maggie Lane, Robert Hale Limited, London, 1996. (ISBN 0709037090)

Jane Austen In Style, (formerly published as Jane Austen's Town & Country Style),  Susan Watkins, Thames & Hudson, New York, 1990.   (ISBN 0500279004)

Jane Austen's World, Maggie Lane, Adams Media Corp., Mass., 1996.  (ISBN 1558507485)

Britain Portrayed, A Regency Album 1780-1830, John Barn, The British Library Board, 1989. (ISBN 0712301747)

Bucks and Bruisers, Routledge & Kegan Paul, London, 1971.  (ISBN 0710069677) (about the Regency sport of pugilism)

Children's Costume in England, P. Cunnington,, Prometheus Books, 1972.
(ISBN 0713603712)

The County Maps of England, Thomas Moule, Studio Editions, London, 1990.  (Reproduction of The English Counties Delineated by Thomas Moule, 1830) (ISBN 1851704035)

Empire Costumes Paper Dolls, Tom Tierney, Dover Publications, 1999.  (ISBN 0486408132)

*The English Country House Party, Phyllida Barstow, Sutton Publishing, Great Britain, 1989.  (ISBN 0750918497)

English Costume for Sports and Outdoor Recreation From the Sixteenth to the Nineteenth Centuries, Phillis Cunnington and Alan Mansfield, Adam & Charles Black, London, 1969.  (ISBN 713610174)

*English Women's Clothing in the 19th Century (A Comprehensive Guide with 1,117 Illustrations), C. Willett Cunnington, Dover Publications, NY, 1990.  (ISBN 0486263231)

*Fashions of the Regency Period Paper Dolls, Tom Tierney, Dover Publications, New York, 1996. (ISBN 0486293351)

The Gentleman's Daughter-Women's Lives in Georgian England, Amanda Vickery, Yale University Press, London, 1998. (ISBN 0300080026)

The Hell-Fire Clubs, Geoffrey Ashe, Redwood Books, Great Britain, 2000.
(ISBN 0750924020)

The History of Underclothes, C. Willett & Phillis Cunnington,, Dover Publications, NY, 1992.  (ISBN 0486271242)

The Lightning-Fast Lexicon of Period Lingo, ($14.95 including first class shipping. P.O. Box 1738, Aztec, NM 87410.  Make check out to Pelican Ventures.)

*Men's Fashion - The Complete Sourcebook, John Peacock, Thames & Hudson, London, 1996.  (ISBN 0500017255)

Our Tempestuous Day, A History of Regency England, Carolly Erickson, William Morrow and Co., NY, 1986.  (ISBN 0688060862)

Peterson Field Guides, Birds of Britain & Europe, 5th edition, Roger Tory Peterson, Guy Mountfort, & P.A.D. Hollom,, Houghton Mifflin Co., NY, 1993. (ISBN 0395669227)

Pride & Prejudice Paper Dolls, Brenda Sneathen Mattox, Dover Publications, 1997.
(ISBN 0486297853)

*The Prince of Pleasure and His Regency, J.B. Priestly, Heinemann, London, 1969.
(ISBN 0434603570)  (year-by-year chronology)

Regency Etiquette, The Mirror of Graces (1811), by a Lady of Distinction

*The Regency Reference Book, Emily Hendrickson

Regency Style, Steven Parissien, Phaidon Press Ltd., London, 1992.  (ISBN 0718434548)

The Reminiscences and Recollections of Captain Gronow Being Anecdotes of the Camp, Court, Clubs and Society 1810-1860, Rees Gronow, Viking Press, NY, 1964.  (no ISBN) (A chronicle by someone who lived during the Regency.)  (This edition has period photographs.)

Captain Gronow His Reminiscences of Regency and Victorian Life 1810-60, edited and with notes by Christopher Hibbert, Kyle Cathie Ltd., London, 1991.  (ISBN 1856260135)  (Covers more than the Regency period.  Neither Gronow book is his entire recollections.)

Slang Through the Ages, Jonathon Green, NTC Publishing Group, Lincolnwood, IL, 1997. (ISBN 0844208345)

Thesaurus of Regency Slang and Idiomatic Phrases, Melissa Lynn Jones, ($29.95--Melissa Lynn Jones, 4914 - 79th Street, Lubbock, TX  79424-3126)

*What Jane Austen Ate & Charles Dickens Knew, Daniel Pool, Touchstone, New York, 1993. (ISBN 0671882368) (Covers the entire 19th century, but I still find it useful.)

The Writer's Guide to Everyday Life in Regency & Victorian England From 1811-1901, Kristen Hughes, Writer's Digest Books, Cincinnati, OH, 1998. (ISBN 0898798124)

The Wordsworth Dictionary of British History, J.P. Kenyon, Wordsworth Reference, 1994. (ISBN 1853263222)

Internet Sources:

The Beau Monde RWA Chapter:  http://www.thebeaumonde.com

British Titles of Nobility:  http://laura.chinet.com//html/titles01.html
http://www.sff.net/people/jobeverley/title.html
Several Sites:  http://history1800s.miningco.com/homework/history1800s/library/bltitles.htm

Bath Assembly Rooms:  http://www.museumofcostume.co.uk/mocpub/assemblyrooms.htm

History of Brighton:  http://tourism.brighton.co.uk/

Bow Street Runners:  http://www.uaa.alaska.edu/just/just110/police1.html
http://www.spartacus.schoolnet.co.uk/LONbow.htm

A British Christmas:  http://people.delphi.com/mariachristm/gbx.html

Clothing:
Regency Costume:  http://regency.tulgey.org/costume/regcostume.html
Regency Fashion Page:  http://locutus.ucr.edu/~cathy/reg3.html
http://austentation.tripod.com/links.html#fashion
The Costume Page:  http://user.aol.com/nebula5/tcpinfo.html
The Costumer's Manifesto:  http://www.costumes.org/pages/regencylinks.htm
A list of many costume sites:  http://www.costumes.org/pages/maincostumesites.htm
The Costume Ring:  http://www.webring.org/cgi-bin/webring?ring=costume;list
Fashions from La Belle Assemblee:  http://www.moonstonerp.com/reglib/toca1812.htm
Le Beau Monde, or Literary and Fashionable  Magazine, 1806-1810:  http://locutus.ucr.edu/~cathy/beaum.html
Bissonnette on Costume Time Search: The Nineteenth Century: 1800 to 1829:  http://www.kent.edu/museum/anne/bissonnette/3timesearch/tsnineteenth/1800-1829/1800-1829.html
Illustrations of Regency Clothing:  http://www.pemberley.com/janeinfo/ppbrokil.html
Millieux Costume Site:  http://milieux.com/costume/
Regency Footwear:  http://locutus.ucr.edu/~cathy/shoe.html
Regency Hats & Bonnets:  http://freespace.virgin.net/martin.holland1/milliner/regency.htm
University of Cambridge costumes (1803):  http://www.costumes.org/pages/1803cambridge.htm
Men's Clothing:  http://regencygent.com/
Royal Naval Dress:  http://users.sisna.com/justinb/rnpage.html
British Uniforms of the Napoleonic Era:  http://www.ar.com.au/~jriddler/sharpe/uniform.html
1810 Rifleman's Uniform:  http://www.southessex.co.uk/uniforms.htm
Russian & Prussian Uniforms of the Napoleonic Wars:  http://russian-prussian.napoleonicwars.com/uniforms.shtml
Jessamyn's Regency Costume Companion:  http://www.songsmyth.com/costumerscompanion.html
http://www.costumes.org/pages/regencylinks.htm
Regency Images:  http://www.sensibility.com/vintageimages/1800s/
Regency Style Year-by-Year:  http://locutus.ucr.edu/~cathy/reg5.html
The History of Costume by Braun and Schneider:  http://www.siue.edu/COSTUMES/history.html

Food and Drink in Regency England:  http://laura.chinet.com//html/recipes.html

Gretna Green:  http://gretnagreen.com/gretna_story.html

Regency Language:  http://www.likesbooks.com/regencyspeak.html

Language of the Fan:  http://www.ideco.com/fans/language.htm
http://hometown.aol.com/FanCollect/language.htm

London's Men's Clubs:  http://members.aol.com/LONDON20/full/belle/whites.html

The London Season:  http://www.literary-liaisons.com/article024.html

The 19th Century London Stage:  http://artsci.washington.edu/drama-phd/19title.html

Manners and Customs:  http://www.stpt.usf.edu/~runge/MasonJA1.html

Military:
Royal Navy during the Napoleonic era:  http://home.gci.net/~stall/ship1.html
Napoleonic Wars:  http://www.napoleonicwars.com/
The Peninsular War:  http://www.btinternet.com/~a.jackson/penwar.htm
Napoleon's Timeline:  http://history1800s.about.com/homework/history1800s/library/timeline/blnaptimelinea.htm
British Merchant Navy:  http://website.lineone.net/~wavecrest/
Horatio Nelson:  http://www.admiralnelson.org/
Old Royal Navy College:  http://www.greenwichfoundation.org.uk/
Land Forces of Britain:  http://regiments.org/milhist/uk/uk.htm

Sex in the 1800s:  http://history1800s.about.com/homework/history1800s/library/weekly/aa093099.htm

List of the British Home Secretaries:  http://history1800s.about.com/homework/history1800s/library/blhomesec.htm

Life at sea:  http://www.nmm.ac.uk/education/fact_agesail.html

Life of the Industrial Worker in 19th Century England:  http://applebutter.freeservers.com/worker/

Regency prints and maps:  http://www.printsgeorge.com/

The Regency Town House:  http://www.regency-town-house.org.uk/

Regency Timeline:  http://members.aol.com/regencyrdr/regtime.htm

Vauxhall Gardens:  http://www.geocities.com/Athens/Olympus/2516/index1.html

Sites with Multiple Regency Topics:
The Georgian Index:  http://www.users.qwest.net/~dwagoner/index.html
The Regency Collection:  http://homepages.ihug.co.nz/~awoodley/Regency.html
Regency Repository:  http://www.geocities.com/Athens/Acropolis/7517/index.html
Letter Writing, Road Transport & the Mail:  http://members.xoom.com/leisurewrite/regent.html
The Regency Page:  http://locutus.ucr.edu/~cathy/reg.html
Maiden Faire's Regency World:  http://www.angelfire.com/il/maidenfaire/
Snippets of Scotland & the Regency:  http://www.inficad.com/~jacreding/jacsnippet.html
The Regency Lovers Café:  http://members.tripod.com/regencycafe/regencycafeindex.html
Links to the Regency on the Web:  http://www.austen.com/onreg.htm
Georgette Heyer Homepage:  http://www.georgette-heyer.com/
Regency Resources:  http://www.heyerlist.org/regsourc.htm
London in the 19th century:  http://www.spartacus.schoolnet.co.uk/London.htm
England Web Sites:  http://home.netcom.com/~toniaizu/d02.html
Historical Cheat Sheet:  http://www.likesbooks.com/history.html
Regency Links:  http://www.belgravehouse.com/reglink.htm
English Culture:  http://hal.ucr.edu/~cathy/231C.html
Regency Library Links:  http://www.regencylibrary.com/links/links.htm
Writer's Resources:  http://www.literary-liaisons.com/resources.html
About the English Regency:  http://www.geocities.com/Vienna/Strasse/1815/history.html
Illustrations from the Extended Regency Period:  http://www.pemberley.com/janeinfo/rgnclfil.html#gen
http://www.sff.net/people/april.kihlstrom/
Jane Austen info:  http://www.pemberley.com/janeinfo/
The Reader's Corner:  http://www.autopen.com/romance.regency.shtml#scoop
http://reenactment.about.com/hobbies/reenactment/msubreg.htm
http://www.strangegirl.org/regency/regencylinks.html
Regency Library:  http://www.moonstonerp.com/reglib/about.htm
The Regency and Post-Regency Period:  http://www.likesbooks.com/regent.html
http://www.sfo.com/~neff/reglink.htm
http://reeanactment.miningco.com/msub20.htm
Links to England Site:  http://pweb.netcom.com/~toniaizu/deng.html
Regency Web Ring:  http://www.mimanet.com/cgi-bin/rings/regency/sitelist.html
http://directory.netscape.com/Top/Arts/Literature/Genres/Romance/Research/Regency
 

Newsletters, e-mail loops, & organizations:

The Beau Monde RWA Chapter has an e-mail loop for members only.

Regency Loop:  regencyloop-subscribe@egroups.com
              Members of the Regency Email List must either have one or more
              Regency books in print and published by a paying, offline publishing
              house or be actively engaged in writing and submitting a Regency period
              novel for publication. A closed (restricted) list, please keep in mind that
              first priority for open slots will be given to published authors.

Regency:   Regency-subscribe@egroups.com
              This is a forum for readers of Regency romances, including historical romances
              set during the Georgian or Regency eras. If you enjoy books, films, and
              television series set during the period from 1750-1820 this is the place for you.
              We enjoy and discuss a variety of authors.

TheRegencyReader:  TheRegencyReader-subscribe@egroups.com
              The Regency Reader, a monthly newsletter for anyone who loves
              romantic fiction with a Regency twist,  is a publication of the
              Beau Monde, a Regency focused chapter of Romance Writers of
              America.   Everyone is welcome to subscribe.

Regency Plume Newsletter:  http://www.freetown.com/Picadilly/HydePark/1073/RegncyPlume.html

The Society of London Ladies:  http://members.aol.com/London20/index.html

Belle Letters:  http://members.aol.com/London20/belle.belle.html
  (has articles on White's, Patronesses of Almack's, Vauxhall Gardens, and more)