Many SCA researchers have shared their research with us.
Of course, Stefan’s Florilegium has a chapter on “clothing”. Many of these are email messages (those with the .msg extension) from a variety of networks. Others (.art extension) are articles on the topic.
Regia Anglorum reenacts Anglo-Saxon, Norman, and British history, 950-1066. They share some good resources as well.
The Viking Answer Lady is a great person to ask about anything Norse.
Hurstwic has an excellent depiction of re-created Viking age clothing. They describe the difficulty of recreating clothing from the scraps found by archaeologists.
Samurai for the SCA Guy and Gal provides an album of Japanese clothing worn by SCA folk. Got silk?
The Elizabethan Costume site provides information about all things Elizabethan. Not late period? The Elizabethan Smock Pattern Generator makes a garment suitable for any period based on your measurements. It really works, and it gets the most out of a piece of fabric.
Baroness Briana Etain MacKorkhill provides a huge list of links for the edification of the members of the Barony of Forgotten Sea, its cantons, the Shire of Cúm an Iolair and the members of the SCA.
Would you like to dress a toddler?
Need shoes? Try Footwear of the Middle Ages.
Some people depend on patterns for sewing. There are a few modern patterns that can be tweaked to make them look period, but there are some people who produce patterns which have been researched. Reconstructing History claims to have the most historically accurate patterns on the market.
If you can afford it, there are some places that sell good well-made clothing. Historic Enterprises offers armor, garb, toiletries, and even a flint and steel for fire making. Revival Clothing has many nice items for sale, like silk hose for about $40.
On a different note, Medieval Material Culture Blog has many good links, and keeps you up to date on exhibitions of period art and culture. They feature “What’s new in what’s old”.
Googling “medieval” will often result in a hit for “Medieval Life and Times” which is poorly written and contains much misinformation. They get their pictures from another site that comes up a lot, a history of costume published in the 1800s by Braun & Schneider. (Some libraries have this in book format.) It’s quite an overview, but it contains many inaccuracies and no documentation.