" OFF TOPIC "Hmm well I can price out a system that would easily run Crysis all maxed out, but what Resolution do you want to play it at? I mean there is a massive difference in Hardware price for a 1280-1024 resolution then a 1900-1600 resolution.
Going SLI is a good bang for your buck ideal, at the same time there isnt a game out there or in the works to take really good advantage of such a thing like 2 8800gt's or even 2 8600's. If you want higher resolutions to be fesible with your gaming rig make sure you buy a 512MB card at the very least, the memory of your card only seems to effect resolution in the end. Other smaller cards can brute force through most settings alone, resolution is a differnt kind of beast all on its own.
Pysics cards at this point dont seem to be worth it from reviews and what I have read.
Net boosting cards I hear are a scam, yet some people will not play without them. Thats a personal opinion I guess.
Difference between 4GB's and 2 GB's of Ram seems to be your tollerence for seeing blue screens vs a small performance hit in load and in game loading " chop ". I prefer the 2GB's of RAM, where many Vista users will sport 4GB's without question. Although I have heard that Vista is more adapted to higher amounts of RAM where XP is not. Thus I would research that if you go one way or another.
Processors, this at them moment is a no brainer. Intel has a lock on the gaming and processing side, even taking into account price. ( Last time I looked this was the case, now it may be differnt) The 4mb L2 chache ( 2x 2MB) on the Core dou's is amazing going from a 4400+ 1MB chache (2x 512KB) to one of these CD's is a big change. I dont think AMD can compete on this feild in raw power yet.
On the mother board side, make sure you get Gb ethernet in your onboard stuff, I also suggest atleast 7.1 surrond also onboard. Sound cards these days our nice if your an audiofile, but you wont hear the difference other wise. I suggest even if you dont go SLI, to buy an SLI board. The option for upgrading is always nice, plus maybe 6 months after buying a top end card it will drop close to 150$ or more.
Ram wise I usally go with Kingston as my buget ram, and Corsair for my gaming RAM. Is there a difference between the 2? In your case probably not, if your not going to chanage RAM timings and try and OC everything, I suggest going with w/e is on sale.
Hard drive wise. What ever is biggest isnt always best. Many drives that hit the 500GB mark have reduced read times, stick with cheeper 250GB drives and make sure of one thing when ever you buy a new Hard drive. MAKE SURE IT IS A STAT drive, ATA drives will have limitied bandwidth and also many new boards like the one I have, will only have 1 ATA port. Many use this for old DVD drives and such.
For a monitor, there really is only the sky as your limit. Most considerd there wallet the limit, but your case may be different. DVI is the best choice outside of HDMI as far as I know, but it would be hard for a person to tell the difference between the 2.
Buy your parts from Newegg.com if you live in the states and MemoryExpress or OEM if your in Canada. Outside of NA i have no clue where to shop.
Hope this helps, but as many have pointed out building a beast of a system usally backfires on you. Architecture of the chips is more important then brute force power, and the only way to upgrade that is to wait and by the next gen or RAM or GFX card.
"On TOPIC " Buy a prebuilt gaming rig is NEVER! cost effective, find someone anyone to show you how to build your own computer. Many stores will slap your Processor to your mother board for free if you buy them togather. Puting in Ram and a GFX card is like putting the Square in the Square shaped hole and the Rectangle in the Rectangle shaped hole.
The only complex part is attaching your case features to your mother board. I have had help with this everytime. Last time I used the manuel that came with my Mother board, it told me to read my mother board which they now seem to have everything labled. Which makes me feel pretty dumb :(