New build RAM query..what to buy??

I have the following parts but am not sure of the RAM to get, I guess I dont understand fully the CAS thing, I was recommended some that was CAS9, pretty cheap, but I see alot of people getting the ripjaw stuff or others....some that have like 6-8-6-12 or somesuch...guess my question is what to get for these parts to work good, OCing would be an afterthought as I dont have a CPU cooler yet besides the stock one, so down the road I will probobly, but for now just getting a solid machine to use and play games with is my goal...

Coolmaster HAF 932
asus p8p67 pro
i5 2500k
GTX 570SC-EVGA
XFX Black Edition XPS-850W-BES 850W
OCZ Vertex 2 OCZSSD2-2VTXE120G 2.5" 120GB SATA II MLC Internal Solid State Drive (SSD)
win 7 home 64


any help and suggestions are appreciated as always....this forum is the best...LOTS of good ideas and data here:-)

thanks in advance:-)