If you're searching for slang spoken by criminals, waterfront rogues and similar low life, check out Cant, my abridged version of the 1811 Dictionary of the Vulgar Tongue. I've organized select words by topic, then alphabetically.
British History Online -- The definitive source for information about everything from the architecture of Almacks to specific political figures.
Commerce
British Money
More about British Money
How Much Is That? -- Calculate how much today's dollar or pound was worth in a specific year.
Pounds and Pence -- British money in the Age of Napoleon
Prices and Wages 1700-1725
Smugglers' Britain --the unedited online version of Richard Platt's excellent resource.
Government/Law
Acts of Parliament - 1837 thru 2009
Introduction to the House of Lords Ceremony --detailed account of the ceremony. It was changed based on the recommendations in this 1998 report.
British Parliament - official website
Nancy Mayer: Regency Researcher -- fantastic resource on law, especially with regard to marriage.
Proceedings of the Old Bailey -- contains accounts of 100,000 criminal trials 1674-1834
UK Statute Law Database
Hearth & Home
Book of Household Management by Isabella Beeton - Late 19th century, but chock full of advice on how to deal with servants and other household issues. Wonderful period recipes, as well as priceless info on what to do with rancid butter, etc...
Decoration of Houses by Edith Wharton-- Written in the late 19th century. Wonderful descriptions of walls and window treatments, floors and ceilings, halls, ballrooms and saloons. Trying to figure out what furniture is in your heroine's bedchamber? This is the place.
Old & Interesting -- a history of domestic paraphernalia with photos of antiques. Particular emphasis on laundry but there is info on cooking and beds as well.
Language
1811 Dictionary of the Vulgar Tongue -- buckish slang, unjiversity wit and pickpocket eloquence by 18th century British antiquarian, Frances Grose.
Internation Dialects of English Archive -- hear different British accents.
Online Scots Dictionary -- English to Scots English translation
Provincial Glossary -- by Francis Grose, author of the Dictionary of the Vulgar Tongue. Includes local proverbs and superstitions.
Writing Implements of the 19th Century -- John C. Loring's excellent display of 19th century pens, pencils and accessories.
Medicine/Science
Calendar-- Need to know what day Christmas fell on in 1814? The phase of the moon for a specific date in history? Check out this site. It can generate calendars for any year and any country.
Climate History -- Meteorology at West Moor's excellent index of weather for England by decade
Even More Climate History-- rainfall in England and Wales from 1914 to present. Figures are in millimeters. Monthly minimum and maximums are calculated.
Domestic Medicine in 1785 by W. Buchan
Making Fire with Flint & Steel -- the procedure for lighting fires in the days before Lucifer sticks.
Nature Online -- from the Natural History Museum in London. English and Scottish flora and Fauna types by postal code. Plant, animal, and insects.
Peerage
British Titles List -- Wikipedia list of extant and extinct titles dating from 1066-present. Includes the family name.
Peerage -- everything a writer needs to know about the peerage system in Britain. Note: this is a modern point-of-view so some policies have changed.
Places
Country House Database -- a list of country houses in the British Isles from the late Middles Ages to ca. 1850. with an index of families.
Leigh's 1819 New Picture of London -- everything the Regency writer needs to know about life in London. From how provisions were supplied, to street indexes, places of worship and public buildings.
London Panoramas -- 360 degree views of select bridges, squares, parks, etc...
Squares of London -- Georgian Index's outstanding site for descriptions of and tenants living in London's residential squares during the Regency.
Vauxhall Gardens -- singers, musicians, performers, proprietors and staff from 1661-1859
Views of London -- views of buildings and squares.
Religion
1662 Book of Common Prayer
Consangunity-- a table of marital relationships forbidden by the Church of England in 1705.
Social
Chambers' 1869 Book of Days -- detailed description of historic events, biographies of famous people, and customs and culture.
Correct Forms of Address - Laura Wallace's fantastic resource of the proper way to address the peerage.
Fashion Era -- Pauline Weston's wonderful website of clothing for all time periods.
Demode Couture -- women's clothing 1600-1919. THE best resource for fashion images from museums around the world.
Gaskell's Compendium of Forms-- Late 19th century but sure to be applicable earlier. Written form of address for letters of condolence and apology, dinner invitations, weddings and balls.
Letters from the Past -- provided by the Victorian Web. Information about postage costs during the Regency period, franking and who paid what. Many fine examples of period letters.
Regency Fashion Page -- fabulous resource of Regency clothing from Cathy Decker who has a Ph.D. in 18th C. British Literature.
Regency Dancing -- everything you want to know about the topic, including dance steps.
Regency Skin Care & Cosmetics -- Yvonne Forsling's excellent website on the topic.
Social England Under the Regency - begins with the corn riots and ratification of the Peace Treaty in 1815 and runs until the birth of Queen Victoria in 1819. Includes lots of illustrations.
Travel
Great North Road -- history and construction of, geology, maps, distances between towns.
Horse/Traveling Facts -- Jean Ross Ewing/Julia Ross' excellent resource on the care and feeding of horses, plus how far they can travel.
Writers Riding Horses - author Judy Ridgley's excellent resource
Inns of Old London-- alphabetical resource of information on the inns of London and other information on historic buildings in Britain.
Multimap -- find the distance between cities in Europe and Britain
1792-9 Map of London
Cary's 1818 Map of London
1827 Map of London
1859 Map of London