Regarding the 2012 USO although his actual tennis wasn't peak level his mental strength in that tournament was absolutely insane- Murray is underrated mentally and in four of the last five matches he showed a ridiculous level of clutch on big points with the ability to take the initiative, especially in the tiebreaks- he saved set points with aces and some ballsy play.
Very encouraging to see after all those times he wasted match points late last year. The way he saved that MP against Ferrer makes that whole crapfest of a match a blessing in disguise. If he can keep it up and combine it with more offense and big serving, he will be mighty tough to beat for anyone.
Maybe he actually hasn't peaked yet
Some good matches already mentioned, but I'd like to put in a word for Wimbledon 2011 SF, where he was leading 5-7 1*-2 15-30 against Nadal before missing that sitter for 15-40, and then completely imploding mentally.
Murray played a very goood match on clay against Gasquet last year in the FO during the last three sets after faking injury in the first (don't get his behaviour last year during the tournament, it maid him a bad image in the french medias I believe).