Fan's and Noise go hand in hand. After much searching I found a nice combination for Maxuim Air flow while keeping Noise level low. The Sunon 80mm KD1208PTB1-6 from Cooler Guy's fit this requirement. Low noise level while Providing more than enough air flow inside my case.

Spec's:

• KD1208PTB1-6
  
• Sunon ball-bearing
  
• 800x25 4 wire case fan.
  
• 42.5 CFM

Test System

Temp's were taken after Running Foldind@Home For 15min
I had 2 Generic 80mm Fan installed in this case, Front fan Pulling air in and rear fan pulling air out. Temps with generic fans were:

Case 80f
P/S 81f
CPU 123f

Not very good Temps for my 1.33g Tbird
With the Sunon 80mm Fans installed I saw a big drop in temps

Case 72f
P/S 73f
CPU 109f

The Sunon's Noise level was not any louder than the Generic 80mm fans I was using but the Air flow and cooling increased greatly I would recommend the Sunon 80mm KD1208PTB1-6 Fan as a very nice and affordable case cooling solution
You can Purchase The Sunon 80mm Fan KD1208PTB1-6 from the Cooler Guys at coolerguys.com