And what do you get for that extra $40? You get a 2GB flash drive that looks like the dog tags of StarCraft's main human character Jim Raynor that contains the original StarCraft game and its expansion Brood War. You also get a 172 page StarCraft II art book, a behind-the-scenes DVD with documentaries, the game's cinematics with commentary and more, the game's soundtrack with extra bonus music tracks, and a copy of issue 0 of the StarCraft comic book. You also get a way to download exclusive stuff from Battle.net like special portraits for your player profile, decals to customize your in-game units and a special version of the Thor unit.
And if you happen to be a World of Warcraft player, you might want to pony up for the StarCraft II Collector's Edition. It also comes with a mini Thor in-game pet for Blizzard's hit MMO. Sadly Blizzard is still not announcing a release date for the game.
Update: We have added a gallery showing some of what's inside the Collector's Edition box
Gallery: StarCraft 2 Screenshots