I guess Rstar will release GTA V in 1 year so you should buy GTA IV: The complete edition if you do not have the same game on PC, and Call Of Duty Modern Warfare 3 would be nice If you have not played Modern Warfare 2 on PC, and If you have played it and didn't like it then get Black Ops, just in case you ever want to play Call of Duty.
:ps: I have Battlefield 3 and Black Ops only, I'm currently waiting for GTA V.