If you want your current PC parts quieter clean the dust out of the heatsinks. Fans run faster if there is cooling issue.
Best no-noise parts in my opinion
PSU: Zen Fanless, NorthQ Pacific, Silverstone Nightjar
Graphics Card: Gigabyte 8600GTS Silent Pipe or PowerColor HD3870 Fanless
CPU: Intel Q9300 Quad or other 45nm Duo
CPU Cooler: Scythe Ninja Plus rev B (cools my Q9300 fanless although came with one)
Hard Drives: Western Digital RE2 or Samsung Spinpoint
Case: Any big tower case with a hole in the top to let the air flow out like a chimney.
If you're gona use fans buy them big 120mm+
Mostly what I used although I've got to find a few quid more for a fanless PSU and make some holes in the top of the case
DinoHunter (still no nVidia compo voucher!), CPU/GPU Benchmark, DarkFish Encryption DLL, War MMOG (WIP), 3D Model Viewer