GTA4 is now released for the PC! From the press release spam:

Developed by series creator Rockstar North and set in Liberty City, the latest installment in the enormously successful Grand Theft Auto series features a painstakingly detailed and life-like city for players to explore; a rich, immersive narrative experience; an original soundtrack highlighting the cultural eclecticism of Liberty City; and newly expanded multiplayer just for the PC.

One of the cool new things on the PC version is the video editor, which lets you record footage in the game (both singleplayer are multiplayer), make real-time edits, change audio, add other effects, etc and then automatically post it to the Rockstar Social Club to brag about it.