Aibell's Garb and Patterns — Instructions, documentation, patterns & more. Specific regions & eras include: Roman, 5th-10th c. Irish; 10th-11th c. English; 15th c. Italian; and 12th c. bliaut. Also cloak patterns.
Anea Costumes — Anea's page with her articles and costumes, mostly Italian renaissance, but also other periods & theatrical costumes.
Briana's Clothing Page — How to make an Italian chemise, draft a bodice pattern, make an Italian ribbon coif, and a Spanish farthingale.
Bronzino Gown — by Danielle Nunn-Weinberg. I love this dress!! Information and construction details, also inspiration portraits.
Milanese Tailors Handbook, A — This site contains images from a book compiled in the 1570s by several tailors. It consists of sketches of men's and women's clothing of that period, along with drawings of the patterns.
My Own Grandpa — Ben Pung's LiveJournal site, which is update more frequently than his website, Lorenzo's Progress. His diaries on Italian clothing he has made, especially from late 15th century Siena.
Oonagh's OwnUpdated! — From the website: "An overview of dress from the 16th century, with a strong focus on Venetian dress of noble women." Mostly Venetian, but also a German gown and a few Elizabethan gowns. Oonagh makes really gorgeous things.
Oonagh's Own BlogNew! — Blog site by Oonagh, which seems to be more recently updated than her website (above).
Philippa's Wardrobe — Lots of lovely costumes from various regions and eras - Flemish, Italian, English, Roman, etc.
Realm of Venus — by Bella Lucia de Verona. "Women's clothing and accessories in 15th Century Venice." Sections include: Venus' Wardrobe, with articles and pictures breaking down Venetian clothing by era; Venus' Seamstress, with pages about the construction; and Venus Adorned, about accessories.
Sugar & Gamurre — Site with loads of information about the 15th century Italian dress. The original site went away with the demise of its web host, Geocities. This seems to be an archived copy of the site.