Hmm...Considering the nehalem is around 10 months away for extreme edition, this is what I'd recommend.
q6600
2x 8800 GT (don't go overboard, the g80 architecture is old, g100 will be around q3/q4)
or a single 3750x2
X38 based board or 780/790 based on your video card choices.
Only go ddr2 ram, ddr3 isn't worth it atm
That's what I'd recommend..Why?
Save your money for Nehalem, considering how vast the performance increase of these new products will be, and how long nvidia has had to tweak their upcoming g100...it would be unwise to dump THIS much money into a rig like that.
This is my opinion though...Use this for a bit, than when Nehalem comes out, nab a extreme edition, which would OBLITERATE the core 2 architecture, after all, they are stating core 2 to nehalem will be an even larger gap in performance compared to the previous netburst to core transition. So you may have a uber rig for a little while if you go all out now, but it won't last as nearly as long by toning your choices down slightly, and go crazy at years end.
Also, if you want, you could go DDR3 now, that way you can migrate it into the Nehalem based board...BUT...prices will drop, best to nab ddr2.
Now I know this is probably NOT what you want to hear, but something like this will handle anything you throw at it (except crysis, but that won't be handled well till the upcoming new architectures, or maybe even the one after that). But this way, you'll have the mac daddy of a rig that will have bragging rights, and peformance to back it up for a while, g80 is old, r700 is around the corner, same with g100, nehalem at years end. If you buy this now, you can brag for 8-9 months on the cpu, and 4-6 months on the graphics cards. When nehalem midranges hit the market (early q1 2009), they will decimate your extreme edition penryn, while in q4 2008, nehalem extreme edition will make the extreme edition penryn a laughing stock. Not much bragging rights if you ask me...=P...
But if you just get something still extremely powerful now, but cheaper, and wait for Nehalem and the new architecture, you'll have gpu's that you can brag about for 12+ months, and a cpu that will hold it's own for 2 years as a extreme edition. much better route that will live longer than wasting all that money now..
Once again probably not what you want to hear, But the safest and smartest way to make sure your rig kicks ass for years to come.