So, what PC gamer "killer apps" exist that call for the purchase of a PC?

[Deviation59]

Killer apps on the PC in the last year or so for me included Crysis, STALKER, Sins of a Solar Empire, The Orange Box, Fallout 3, Bioshock and The Witcher. Sure, three of those were on consoles as well but the PC versions were unquestionably better if you have a decent gaming rig.