#2: Braid, Cortex Command, Machinarium, Osmos, Revenge of the Titans
#1: World of Goo, Aquaria, Gish, Lugaru HD, Penumbra Overture, Samorost 2
Steam codes are currently available for the first 150,000 or so people. Samorost 2 is on Steam but it isn't included. Cortex Command and Revenge of the Titans are not on Steam yet. When they are, they'll be automatically added to those who typed in their code.
The bundle ends in a few more days.
The addition of World of Goo was a big thing for me, I've had a Wii copy for a while and was excited to get a PC version -- then they went and made it available on Steam which I also wanted. Good times.