Darren Collison, James Posey, and an S&T'd Josh McRoberts for Tony Parker
Why for IND: Parker will be 29 and the start of next season so still probably has at least 3 seasons left before the inevitable decline. He is a three time All-Star and multiple NBA champion so his experience in the playoffs would be invaluable.
Why for SA: If SA is serious about rebuilding, they may to shed Parker's huge contract, which has four years left and will be the largest on the team after Duncan retires. They desperately need athleticism, and McRoberts would instantly become by far the most athletic guy on the team. Collison is a high character point guard who has shown a lot of signs that he'll be at worst a solid starter in the NBA, he'd benefit immeasurably from a coach like Popovich.