Happy to be of service, MA in Costume and Textiles, not that it ever ever helped me get a job, but...you can always type in the garment name in google and punch in images and see what pops up. Check wikipedia etc...
Do be careful to check whether the garment name was actually in use at the time of your setting or a modenr invention to describe old clothing. Some terminology changes over time like stays to corset between the 18th and 19th centuries.
I'll spare sending you to web sites and give you some good hard books to pluck from Amazon or your library,
20,000 Years of Fashion by Francois Boucher.
http://www.amazon.com/Fashion-History-Costume-Personal-Adornment/dp/0810916932/ref=sr_1_1?ie=UTF8&s=books&qid=1269174646&sr=8-1
400 Years of Fashion by Avril Hart (from the V&A)
http://www.amazon.com/400-Years-Fashion-Natalie-Rothstein/dp/1851773010/ref=cm_lmf_tit_9_rsrssi1
These are 2 good survey books with a broad overview of western fashion. For other parts of the world or time periods, you'll need more specific books.