Say it again: HEY, WIKI!
My apologies for getting that bit of the '80s reverberating through your noggin, but it'll be worth it if you don't already know about one of the best vintage sewing pattern resources available on the Web: the Vintage Sewing Patterns Wiki.
That's right: it's all vintage sewing patterns (pre 1990s), all the time. You can search by pattern number -- browse your favorite era -- browse your favorite styles. For fun, hit the "Random Page" button. When I did it today I was rewarded with this lovely pattern:
Since it's a wiki, you can add your own entries and edit others. Share your collection and make me drool! Looking for a certain pattern? Check the "Source/Vendors" link for on-line shops carrying it. Still can't find it? Stick a "wanted" notice on a sewing pattern entry to let the world know your desire.
Vintage ephemera like sewing patterns are, well, ephemeral -- and what I adore about the wiki is that it gives us all a place to preserve and share these bits of history. Check it out!