A single Noctua NF-P12 would suffice for the CPU. Change the rest of the case fans to Noctua NF-S12, they're much quieter. And like justanoob said, accelero S1 would do for the graphics card.
Wow nice guide, and a quick question:
My case has a space for 2 (what i suspect to be) 80mm fans, should i go ahead and full those? they are the back of the case and i guess one would pump air in and the other out.
My pc will also be under a desk.
Another thing you might want to consider adding to the Other Recommended Products section: bitumen. Bitumen is versatile and can be used as noise insulation, they even use it for that very purpose in cars and dishwashers. The advantage it has over foam is that you can use thinner layers.
The power supply fan and CPU cooling fan are usually the main sources of computer noise. Fans and hard drives also produce vibrational noise that's magnified by the PC case or the surface it's sitting on.... get more info at: http://uurl.in/77cpo