I work at Fry's so everything on this list is at discounted rates; this is supposed to be a $1000 build that's supposed to be extremely cool thanks to the oven called my room but I don't mind shelling out extra money for some bells and whistles. All prices listed are how much I get it at Fry's or Newegg not factoring in MIRs.
Miscellaneous -- optical drive, fans, thermal grease, etc. ($50)
Some items at Fry's is actually better than my discount (factory price plus 10% tacked on) so I've been slowly collecting all of the parts over the past month or so. The Q6600 is a tentative pick depending on what's in Intel's RetailEdge bundle pack this season but chances are it'll be returned or sold off around that same price.
The real world performance differences between PC6400 and PC8500 RAM arent noticeable in normal PC usage.
THG's http://www.tomshardware.com/reviews/ram-speed-tests,1807-15.html Ultimate RAM Speed Tests has the details.
2GB vs 4GB benefit is more dependent on which OS you're using. 2GB=XP and 4GB=Vista. It's also dependent on how you use your system. Frequent heavy multi-tasking argues for 4GB where a dedicated gamer can easily get by with 2GB when using XP. And you can always add more RAM later.
Good selection of hardware. You could easily step down a size in PSU (Corsair 520HX) if the price difference looks attractive to you.
Everything looks good except the memory, you will barely see any difference at all (if any) between ddr2-800 @ 1:1 and faster clocked ram. Hell, if you don't overclock you can use ddr2-667 if you wanted to
The reasoning behind getting 4GB PC8500 right now is that every place I'm gone to for that specific memory only has the 2.1v versions and if I were get only 2GB now the only ones on the market later on presumably will be the latest revision at 1.2v. Just about every report/review out there that mixes both of these voltages usually end up in the mobo being fried after a while.
It wasn't long ago that 2GB of RAM was considered overkill whereas it's the standard now not to mention that there isn't a negligible difference in price between 4GB PC6400 and PC8500 -- $95 vs $110 respectively.
I do plan to overclock but that's in the long run depending on my room situation.
P.S. Fry's had the 620HX for $120 after MIR so it was a good deal I couldn't pass up.