I would get Red Dead Redemption immediately (assuming you are talking about the full game). I don`t know how much it costs in MS points, but if I had enough left over I would go with either AC2, Bioshock, or B:BC2 Vietnam.
Sean Aaron ~ "The secret is out: I'm really an American cat-girl."
Q: How many physicists does it take to change a light bulb?
A: Two, one to hold the light bulb, the other to rotate the universe.
Just Say No To Toast!