Cover Browser: over 5000 comic book covers
The Cover Browser showcases over 5000 comic book cover illustrations. There’s everything from the famous first appearance of Superman to Daniel Clowes’s Eightball with new content being added all the time. Seeing the most recent cover of MAD Magazine on the site however, saddens me that Alfred E. Neuman is almost nowhere to be seen (look carefully… he’s been reduced to a mere icon disguised as Pacman).
Ahh, but for true comic book geeks there is the Great Comicbook Database:
http://www.comics.org
Thousands and thousands of covers, summaries, and credits. You can look up stuff by publisher, artist, penciler inker, writer, title. They’re a little light on the alternative press titles, but its still a great resource!