^ Iron Dreamer gave some really good tips there. Which is the main direction I am heading, microATX, which you should consider. I really have no reason to actaully do it since my Asus P5B Deluxe Wifi mobo is working so good, but I just killed my Enermax Charka case so I'm taking the opportunity. I'll be purchasing a that Asus G35 mobo and their microATX case as well. And bring everything over from my old case. For me this is a downgrade, but my guess is the two mobo will perform similar (if not I might have to box it up and return). I won't be concerned since I don't play any new games anymore. This seem to be the trend today, to get everything smaller.
Unfortunately there is no microATX mobo that uses DDR3 rams, so if you are going to purchase a microATX case, I highly recommend waiting to see if there will be one that support DDR3 soon. And even if you do get DDR2 rams, it is cheap enough to invest in speed at higher than 1000mhz. In some rare case it is possible for a ram with lower timing to beat a faster ram with higher timing. Patriot offer the most affordable ram at best peformance, but generally not for overclocking. Crucial higher end rams are pretty good too. Oh god, I remember purchasing that Patriot 5-5-4-9 for $294 a year ago. It really makes me want to cry.
The main concern for me is how well a 135mm PSU fan and two 80mm are going to cool a microATX case with a 8800GTS, my past experience is that PSU with 120mm fans cool extremely well. You only need super cool temp because it is exaggerated in the gaming market, it is not a necesity for a cpu to run at 100*F at all time. I highly recommend buying the expensive Scythe or Enermax fans, they have fans rated below 10db and should be inaudible. You said "gaming" in the thread title, which indicates good video cards, it will be difficult to get them to be quiet unless you buy a fanless card or water cool it, or some very expensive aluminum case. I use the software RivaTuner (there isn't a reason to get ATI card right now) to control the fan speed.
As for PSU I think this market is really overpriced, especially some $150 ones that still use cheaper capacitors, but don't waste money on more wattage than you need. For example, I think SLI is redundant unless you are that much into gaming, it is cheaper to buy a single very expensive card, than the SLI path which rewuire you: an SLI mono, two cards, a very expensive PSU, ending up costing much more electricity, and only average 25% gain of performance for 3d graphic. Don't concern too much with the "80 PLUS" efficiency tag, it is just a marketing thing to make the product cost more (ie THX). My current PSU uses two 80mm fans and was a bit noisy so I installed my own 10db Enermax fan to my PSU and connect it to my Zalman 6 fans controlller, along with all other case fans.
The first Geforce9 card is already available, I would not buy an 8 series card right now and wait for more of the 9 cards to be released. Since the 8800gt is such a big hit, the best in term of performance and value in the 8 series, maybe wait until the 9800gt comes out.
Also about CPUs, I highly recommend getting a quad core, it is cheap enough now. There is a good performance increase in term of allowing many softwares running at once. The Core2Quad E6600 is only $250 now, and there is also the cheaper Xeon 3210 that works with the standard 775 socket mobo too, so for me it is a much better value than spending $200 on a dualcore at the same speed.
Overall I think the most afforable and versatile solution for a quiet computer, if you get an Enermax Charka case which has a 250mm fan and use a 120mm PSU for exhaust, I beleive that will be the only two fans you need in the whole case to keep everything cool and quiet. I don't know what harddrive people uses, but I never ever had issues with noisy HDD, not 7200rpm anyway, my Western Digital is also quiet except for those fast read or writes that it makes the not so loud grinding noises, which is actaully fun to listen to. If you partition it right and stretch the work load between two different harddrives or array then it would be much smoother.
