Recently I’ve seen a few highly desirable books that reproduce book covers - for example this great collection of Japanese cover designs on Amazon - but they tend to be pricey (that particular one is out of print and going for £150+ minimum at the moment, so it might be cheaper to simply buy all the books it features).
But as usual the internet has a solution for the penny-conscious - many, many solutions, but I particularly want to draw attention to the Book Cover Archive, a glorious melting pot of over 1,000 contemporary designs with publisher, designer and typeface information all nicely hyperlinked up and indexed, so you can track how many time Verdana has made it onto the cover of a book (which is zero, so don’t bother, and the same is tragically true of Comic Sans).
I’ve also enjoyed the beat generation archives provided by the seemingly anonymous benefactors at books.rack111.com - check out their fascinating collections of Burroughs, Kerouac and Cassady covers, which I found via the blog of designer John Coulthart, who regularly posts such treasures (along with the occasional slice of gay erotica, so take care if browsing alongside your homophobic aunt).
You can also make us of Librarything’s extensive collection of covers - though only, I think, for a specific title. Here’s their gallery of 1984 covers and a round-up of Lao Tzu covers. Just search for a book and use the ‘Covers’ link to find more.
And of course Flickr is a natural home to such projects - here’s a wonderful collection of Penguin and Pelican covers that user Joe Kral has created. You can always rely on sociology texts to have a cover you shouldn’t stare at prior to shaving.
Wow! Please post the magnificent details of any other cover galleries you’ve found and dug in the comments.