Mobygames is, of course, another good source for such things.
Terra Nova is an example that springs to mind.
I'd like to see some kind of photo collection as a standard component of a GOG download. Whether it was a slide-show built into the installer, or just a bunch of images added in a sub-directory when you install the game, or (more likely) simply put up for download alongside the soundtracks etc.
It would really assist that whole nostalgic feeling of buying a new game back when boxes were big and pretty, and contained decent manuals! (Not to mention ye olde cloth maps, and other goodies...)