Ok I am getting the opportunity to build my brother a really nice machine (hes a gamer) for christmas. When I first started speccing the machine I was going with a core 2 quad 2.83 ghz machine with a single GTX 280 and 8 gigs of ddr 3. However, now with the i7s out I have shifted to an i7 build with 12 gigs of ddr3 (CORSAIR XMS3 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)) and again a single gtx 280. The total build cost is about 2100. However, I have also thought about just building him a midrange system using an amd phenom x4 with 2 4870s for about 1700.
Don't forget that SLI scales perfectly with X58 due to not having to rely on Nforce chipset anymore, so you might see better performance if you go with two GTX260 Core 216's instead of a single GTX280 or HD4870x2.
so what video card would you get? Tom's Hardware has a review with the gtx280s and 4870s (non-x2s) in both single, dual, tri, and quad setups with extremes and i7s and it seems the gtx280s perform better than quad 4870s.
I prefer the ATI cards for several reasons (some of nVidia's business practices, can get a cheaper non-SLI-patched X58, DX 10.1 that we're going to be seeing more of before Windows7/DX11 = better for the long term).
Grab a 1000W Antec Quattro or Corsair PSU so you can run two down the road (or right away if you want to buy them both now). What size monitor btw?
You can also consider only getting 6GB of ram now and adding more later as I imagine DDR3 prices will be the fastest to drop of the new i7/X58/DDR3 items.
I'll throw the new Coolermaster 932 HAF case in there for consideration if you're going with a full tower case. It's got a good price and tons of airflow if you guys decide to try a little overclocking - which you should! And in the case, grab a direct contact heatsink: Xigmatek, OCZ Vendetta 2, Sunbeam Core Contact Freezer.
Also, I'd switch up the HDD for a Western Digital 640GB. Very fast drive and quiet, check out some reviews it's a home run.
I like the i7 build as a no compromise PC.
I think 12gb is unnecessary for a gamer. 6gb is just about right. You can always add more later.
Use the savings to get a 300gb velociraptor for the main hard drive. If that is not enough, then add a slower drive for overflow and backup.
The Antec 1200 is a great case. It is much bigger than what you need to hold your parts, though.