These are worldbuilding sites where I like to do research, presented eclectically, and in no particular order.

Herbs and Medicines

Folk remedies Some of these are hilarious. Try searching baldness or pox.
Stephen Foster herbal and medicinal plant photography
A practical herbal
Herbalism links
Curtis Botanical, an early botanical magazine
Gardening and Herbal Arts, from the SCA
The Wellcome library: history of medicine
Culpeppers Herbal

Other Cultures

Aztec culture
Nahuatl Culture
Encyclopedia Mythica, of folklore, myth and legend
Regency England: it’s not exactly another culture, but close enough. This is a pretty substantial set of resource links
Internet African History Sourcebook
Internet East Asian Sourcebook
Internet Ancient History Sourcebook
Victorian London Dictionary: includes a lot of information on daily life, government and culture

Skills

Tanning the infirm way: Native American Technology and Art
Making Fire With Flint and Steel
How Stuff Works

Regency England

Regency life
The Town Bronze includes info on fashion, dancing, cards, etc
A Regency Lexicon
The Regency Fashion page

Sailing and Ships

Sailing Ships archive
Sailing Ship terminology
Historic Ships
Nautical dictionary
Russian River Ships
Piratical Language
Pirate ships
Deck Configurations
Sail Configurations

Titles of nobility

British titles: an intro to peerage
An explanation of British titles
European titles

Language

The Language Construction Kit: construct your own language
Etymological dictionary
Georgette Heyer Slang and Cant
Regency Slang dictionary
Lexicon of Thieves Cant
Antique words: or words of changed meaning by C.J. Cherryh
A Dictionary of Slang: links to many slangs and other specialized language dictionaries (huge list, a must explore page)
Another list of links for slang dictionaries. Quite different from the above and very worthwhile
Maledicta’s listing of slang and cant dictionaries–extensive and yet be careful, lots of vulgarity and rudeness here.
1811 Dictionary of the Vulgar Tongue

Castles and Medieval Life

Shire of Heronter
Internet Medieval Sourcebook
Castles of Britain learning center
Costume Gallery’s online research gallery
Medieval demographics (a really useful site)
The Food Timeline
Weald and Downland open air museum–offers virtual tours
Life in a medieval castle
Life in Elizabethan England
Renaissance Magazine

Finding Names

Name Sites
Medieval Names: Anglo Saxon, Old English and Anglo-Norman
Medieval Names: names from other countries
Academy library: a source for names from SCA
Behind the Name: etymology and history of first names

Birds and Animals

Birds and Feathers: Native American Technology and Art
The Falconry Centre
Abdereen Bestiary
Deep Sea Bestiary
Horse confirmation and other details about horses

Forensics and Police Procedure

The Writers Medical and Forensics lab Run by Dr. Lyle.
The Graveyard Shift All about police prodedure. Excellent blog.
Police procedure for mystery writing

Medieval sources

Internet Medieval Sourcebook: full and partial texts, background information, religious information. Hosted by Fordham university
A Boke of Gode Cookery: medieval food
Medieval Europe
A Medieval Town dictionary of terms.

Maps

Old London Maps
Mapco Maps
Historic Maps

Fighting and Warfare

Glossary of Fencing terms
Historical Swordfighting terminology
Sword Terminology
The Arador Armour library: Includes a lot of how-to information on making armor
Medieval Warfare
Tour Egypt: the equipment of Pharaoh’s military by Troy Fox. Good pics and info
Historical Weapons

General

Charlotte Dillon’s resources page. Amazingly extensive covering all sorts of time periods and concepts
History of epidemics and plagues
Mysterious Britain includes stuff on folklore, paranormal, ufos and so forth
How much was that worth in past dollars or pounds? A converter of sorts
Fabrics: what kind and descriptions, plus a whole lot of other glossaries. Well worth perusing.
Movement: A useful site about how far various animals and things can move in an hour or a day. Well worth perusing.
The Bodleian Library of Broadside Ballads includes sound files
Ballads

Fairies and Mythological Critters

The Secret Commonwealth of Elves, Fauns and Fairies by Robert Kirk and Andrew Lang (1893), full text
Gods and Mythology of ancient Egypt
British Goblins: Welsh Folk-Lore, Fairy Mythology, Legends and Traditions by Wirt Sikes (1880), full text

The following are some useful links to writing, being published,
and the industry, in-genre and ex-genre.

Landing an agent by Robert Sawyer
Agents discuss the publishing biz
Holly Lisle’s homepage–lots of great information and resources
Holly Lisle’s Resource for Writers: an online newsletter about writing
Bibliomania: full-texts, study guides, more.
Writer’s Weekly
Sentence Sense an online grammar handbook
Internet resource for writers: Lots and lots of links
For Writers lots of useful information including markets and agents
Funds for Writers
Pike’s Peak Writers conference for commercial fiction writers
The Writer Gazette
The Renegade Writer for freelance writers
Preditors and Editors
Guidelines for building a fantasy world by Patricia Wrede
The Writer’s Life resources and articles relating to electronic publishing
Writing World
Writer Tara K. Harper’s website, with substantial material on writing, publishing, finding an agent, and so forth.
Ralan’s Webstravaganza: a guidelines site—up to date and complete
SFF.net has newsgroups and information, as well as a lot of writers’ sites, including mine
SFWA list of writers organizations and resources, this page includes information on agents, writing, research and software
Bartleby’s style corner
Karen Fox’s homepage, with romance links, writing information, and publishing information
Writers Pocket Tax Guide

Blogs worth reading

Whatever: John Scalzi’s very cool blog covering politics and writing and everything inbetween and outside
Jennifer Jackson’s Blog she’s an agent at the Donald Maas Agency and has interesting things to say
Pubrants: another agent blog—good information
Romancing the blog talks about romance writing and has entries from editors and agents, and is very illuminating.
SF Novelists SF and F writers talk about writing and books.
Novelists Inc. A blog by romance, mysery, f & sf writers and industry experts
Magical Words Several SF and F authors talking about writing and the business of writing
Bookends Literary Agency
Writer Unboxed talks about writing
Lucienne Diver my agent’s blog