List is too long for woot's description page.
Quick rundown of GOG:
-Cheap, older games
-Install files are redownloadable in the future
-All games are XP/Vista compatible
-Many of the games come with downloadable manuals/walkthroughs/music/other bonuses included for free
-Not region locked, same prices worldwide
There's also a couple free oldschool adventure games floating around the site for those inclined.