This is such a frequently discussed issue...the quiet computer. Its an easy fix though....
Heatsink: buy the biggest one you can.
Heatsink fan: buy the quietest one that still sufficiently cools the CPU.
Power Supply: shell out $$ for a quiet one, or take your current one and replace the noisy fans with quiet ones.
Case fans: realize that your 8 case fans are the product of crazy computer forum chest beating, and whittle them down to 1 intake, 1 exhaust. Cut a hole in the side panel and build a duct to the HSF. Thats all you'll ever need. Case fans will never make the air colder than the air outside the case, so cut out the middle man and go right to the source.
NMB and Panaflos are indespensible for the quiet computer. You could have 10 NMBs in your case and you'd never know it from more than a foot away. Panaflos are a bit louder, but push a little more air.
For your HSF, what could be better than a YS Tech adjustable? You crank it up during Battlefield 1942, and turn it down at night so it doesn't sound like you're sleeping in a Huey.
For your HS, check out the Thermalright family. Great stuff, and reasonably priced.