Now GameSpy is buggering off, which games would you like to see brought on to Steam?

One of the big titles affected is Halo: Combat Evolved and the custom edition, so much so that there's even a petition. Check out this article:

http://www.ibtimes.co.uk/halo-combat-evolved-fans-seek-support-valve-continued-multiplayer-experience-1443729

This wouldn't be too much of an issue for 1 and 2, as they exist for the PC. The only issue would be porting 3 and 4, these games existed mainly to sell Xbox's. Would they put in the worth the effort on Bungies part?

The way it stands we already know that Games for Windows Live is going the way of the Dodo and now GameSpy is doing the same. Should Microsoft and Valve put aside their differences and consider bringing the Master Chief and his friends to Steam? More importantly if the Halo games did come to Steam would you buy them?