With a 2600 you won't be overclocking so I would buy the fastest 1.5v 8GB (2x4GB) memory modules you can find.
Newegg.com - G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17000) Desktop Memory Model F3-17000CL11D-8GBXL
or these
Newegg.com - CORSAIR DOMINATOR GT 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 2133 Desktop Memory Model CMT8GX3M2A2133C9
Newegg.com - G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17000) Desktop Memory Model F3-17000CL11D-8GBXL
or these
Newegg.com - CORSAIR DOMINATOR GT 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 2133 Desktop Memory Model CMT8GX3M2A2133C9