DO NOT EVER CHEAP OUT ON THE POWER SUPPLY UNIT.
That thing goes, and the entire rig can go with it. Go with a PSU from Corsair, Antec, or a good company like that, and make sure it has enough wattage to run the rig, you can check here
Now that we have that out of the way...
Currently, 8GB is overkill in the RAM department for gaming. 4GB is plenty for gaming. Also, most people here would suggest G.Skill RAM
(that's just one of their sets of RAM).
Also, there is already something built into your motherboard for networking, no need to spend money on a network card.