Possible memory problems?

Hi, I built my first computer recently (november 2010) and it works well. I have windows 7 ultimate x64 and I think I might be ahve some memory issues. I got the BSOD about a month after I finished building it and I thought it was a one time thing, but It keeps coming back every 1-2 months and it usually occurs on resuming from sleep mode. I have also had an error a couple times that make me close all running programs except the explorer and i can't start any programs but rebooting fixes it. I'm going to try memtest86 but I was looking for any advice on what could be cause my problem. I have 8GB ddr3 Ram at 1600mhz here are my specs:

Asus m4a79xtd evo mobo
amd phenom ii x4 965 3.4Ghz
8GB g.skill ripjaw RAM ddr3 1600mhz
Sapphire ati hd 6870 1gb
640gb WD caviar black
Windows 7 x64 Ultimate

If there is anything else im forgetting let or any more info needed let me know
any help is appreciated.
Thanks