Museums - Some links to good on-line textile/costume collections (links will mostly take you to the search page):
The Los Angeles County Museum of Art - search by timeline on 16th and 17th century.
The Victoria and Albert Museum - best if searched on large categories such as "embroidery" - many museums, and the V&A is no exception, use keywords that are not neccessarily intuitive, and if you get too specific, you may not find what you're looking for. The wider search, though more time-consuming, is often more rewarding.
Manchester City Galleries - An under-used resource of 16th and 17th century accessories, such as gloves and bags, and the location of a truly gorgeous blackworked jacket.
The Cleveland Museum of Art - an excellent textile resource. Check through their whole textile collection for pieces of 16th/17th century fabrics.
The Boston Museum of Fine Arts - very large collection of 16th/17th century accessories and clothes.
The British Museum - use their COMPASS search engine for their online collections. Not much clothing from England, but search on "Tudor England" and "Jewellry" (English spelling) for excellent small accessories. Also a good source of dress accessories from earlier times - they have the best collection of online images of Roman and Viking finds.
The Metropolitan Museum of Art - a small but informative section called "timeline of Art History". Most of the collection is not on-line.
Museum Link - a collection of links to museums across the US, sorted by state.
The Embroiderers' Story at Plimoth Plantation - Come see a historic project as it unfolds - a 17th century embroidered jacket using materials correct to the period, including specially made threads that have not been manufactured in nearly 400 years. It's an exciting project, and they have featured my Maidstone jacket reproduction in their blog!