do NOT get a x600 or x700, they are OLD OLD, the 6600GT is a great card, and if you really want a ATI i say get a x800GT like stryker, if you want to spend a little more you can get an x800xl which is cheaper then a 6800GT but is about the same, maybe a little less, BUT NO SM3. anyways, nvidia is the way to go for the time being. you can get some nice corsair valueselect ram 512x2 DDR2- pc5300 for around 98 dollars
im not sure if you are going to OC but the corsair valeuselect is excellent ram.
heres the corsair valueselect, and its faster then that geil ram you have
very nice very nice