I'd go for a AMD phenom ii x4 and spend the remaining on 8gb and 6870 but that's just me.
Get the 6870 with the $25 after rebates saved though .
I will not purchase or recommend an AMD CPU to anyone with a budget > $500 until BD is released. And even then, who knows, since the performance is still an unknown. I believe I've heard that MMORPG games (I don't play them myself, nor am I interested) are pretty CPU intensive, another reason for the SB chip. A 6870 is probably within reach, I'll know on Nov 1 when he tells me exactly how much he has to spend. 8GB of memory is ideal, and again, I will know if that is doable in a few weeks.
I also don't figure rebates into a budget because they are an unknown, even when everything is properly filled out.