A general rule of thumb is if your using 40% of your RAM just at normal/idle conditions you need double the memory.
I Plan on buying me more RAM specifically Crucial Ballistix Tracer 6GB (3 x 2GB)
just cause I want a little more bling to my case
And probably 2 1TB of SAMSUNG Spinpoint F3 in RAID 0

Read many good things about theses hard drive's performances