Bodlian Library- Oxford University's electronic manuscripts
The Grand Register of Robert Bagrit- A huge site with tons of reenactment groups, mostly from Eastern Europe. If you don't want to dig around museum and library sites, this is the place to go. Lots of high quality pictures of good kits
The UK Living History website- A case of why reinvent the wheel. Links to groups worldwide, sorted by period. Also has forums where you can ask questions
Osprey Military- good overviews, take the artist's interpretations with a grain of salt, use the bibliography to dig deeper.
Daily Life in Elizabethan England by Jeff Singman
Daily Life in Chaucer's England by the same
Daily Life in the Middle Ages by the same. Has some similarities to the Chaucer book, but covers a wider time period and isn't as Anglocentric.
Life in a Medieval City by Francis an Joseph Gies. Part of a series of books on medieval life. The others are Life in a Medieval City and Life in a Medieval Town. the Gies' have written several books on the middle ages.
The Burgermeister's Daughter by Steve Ozment 16th century German town life seen through the lens of a scandalous court case.