Officially up to 1333MHz is supported, but you shouldn't have any problem running 1600 or possibly even higher speed memory with it assuming your motherboard supports these higher memory settings. With the latest AMD chips I think 1600MHz is the "sweet spot" with higher speed memory seeing diminishing returns and not gaining you much more performance, not sure if that's the case with SB, though.
Just be mindful of RAM voltage when shopping, I think Intel recommends a max of 1.6V memory voltage with their Sandy Bridge chips, and some higher speed DDR3 kits are rated for 1.65V. Probably wouldn't hurt to run 1.65V DDR3 with SB, but since there is plenty of 1.5-1.6V memory out there might as well just get one of those sets IMO to stay on the safe side.