I'd step it up to DDR2-1000/1066 at least. If you get the DDR2-1066 Corsair Dominators they come with the fans. Another good choice are the Mushkin Redlines.
Also for your Graphics Card(s): HIS Radeon HD 4870 x 2 if you can wait if might be a good idea to get just one HD 4870x2 Rev2 instead (Aug 12th)