gta iv, got it for xbox, years later got it on steam when it was on offer £5.00 i think for gta iv and the 2 expansion packs =p
fallout 3, got it for xbox then i saw the amount of mods for it, so got the pc version
cod 4, got the pc version first but i got the xbox version off a mate
i usually go by the rule that, if i recon or know the game is gonna have or support mods on the pc, i get the pc version, if its gonna be a crappy console port, mite as well get the console version n skip the crap, sadly this is true with many games these days