The Metal Gear Solids 1, 2, 3 and 4
The GTAs 3, VC, SA and 4
The SSXs 1, Tricky and 3
The Hitmans - 2, Contracts, Blood Money
Those I think are my most replayed. Think the MGS games are like 4 or 5 times each. The GTA games 3 or 4 probably. The SSX is a trickier one, get it, where you can just load up your save and play whatever you want. The Hitman games were replayable until you get Silent Assassin in all missions so they fall into the SSX kind of replayability.
I'd add in Mass Effect 1 - must have played that 5 or 6 times now I think about it. I think it has to be 3 or more playthroughs, for me, so a lot of games I've played twice I'll leave out.