I frequently post about vintage stores that don't carry obviously vintage items, but some women really want to look like they stepped out of a period movie. (I completely identify. I love to dress like a 1950s housewife and flit around the grocery store. The ladies at the deli find it delightful.) If you're trying to figure out how to make your retro style just perfect, the new-fangled internet is one of your best sources.
-- Art Deco covers fashion of the Jazz Age through portraits of celebrities and freshly discovered fashion plates. The same bloggers has similar sites for the Flapper and Edwardian periods.
-- Find detailed galleries of fashion illustration from the 1920s-1950s at the clearly named site 1920s-fashions.
-- Study fashion from 1900-1990 at The Costume Gallery. This website even includes full scans of antique and vintage fashion books and catalogs.
-- Fashion Pictures focuses on the 1950s-70s.
-- Be inspired by everyday people from the Life archives.