I'd love Raja Bell for what is left of the MLE. He has slowed down and isn't an elite defender but he'd still be the best perimeter defender on the team. Even though he's only 6-foot-5, his toughness would allow him to play small forward in San Antonio's system. On offense, he's a very good three-point shooter.
He's the closest thing to a Bruce Bowen or Mario Elie that is still on the market. Add in the fact that he's not afraid to rough up Kobe and Bell is far and away the best the Spurs could get with their remaining cash.