What kind of video card do you have? Do you have one, or two?
What kind of PSU do you have?
GA-EP43-DS3L - $100, one PCI-E 2 slot
GA-EX38-DS4 - $225, two PCI-E 2 slots (Crossfire), RAID
If your video card is an nVidia, get the DS3L, don't try SLI.
If it's an AMD, get the DS4 and do Crossfire now or later.
The difference is that Crossfire on X38 is much safer than SLI on an nVidia chipset.
RAM: 2x2GB DDR2-800 $80
Nice case and CPU.