This memory has great reviews and according to corsairs memory finder it is compatible with your mobo and it is 1.5v so there is plenty of overclocking capability. 4 gigs will run xp, vista, and 7 while playing any game, so dont worry about that unless you are running several memory intense apps at one time. I also agree with 4745454b but if you do want 1600 for a future rig I also added a link for that to.
CORSAIR XMS3 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)http://www.newegg.com/Product/Product.aspx?Item=N82E16820145251&Tpk=TW3X4G1333C9A
CORSAIR DOMINATOR 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)http://www.newegg.com/Product/Product.aspx?Item=N82E16820145297&Tpk=CMP4GX3M2A1600C8