Hi,

The stock cpu fan for my Intel E8400 (LGA775) has been getting noisy and I'd like to replace it with an aftermarket one. I have a Coolermaster CM690 case (http://www.coolermaster.com/product.php?product_id=2908) so I should have room for a 120mm fan, I think. I'd also prefer not to spend more than $30. Thanks!

If CoolerMaster's your game, look no further than the Hyper 212, http://www.coolermaster.com/product.php?product_id=6636. Reviewed at SPCR here: http://www.silentpcreview.com/fenrir-hyper212.

Just be prepared to replace the fan. Most of us should have an extra lying around anyway, and good new ones don't cost that much (see Arctic Cooling or Nexus or Noiseblocker).

+1 for Dau_Saunamies.

If you want to save some money and don't mind a bit of noise, then consider an Arctic Cooling Alpine 11. There's a standard version and a "Pro" version and then a cheaper "GT" version. At idle (~500 rpm) it is dead silent. During load the fan will need to run a bit higher, but it will still be very quiet. Click on the link in my signature if you want to read about my personal experiences with the Arctic Cooling Alpine. (I have the Alpine 64 Pro, the AMD equivalent to the Alpine 11).

The CM range is pretty good as above you are better served replacing the fan though (lots of choices at various prices) I use either the 212 or the TX-3 models for most builds both are good and reasonably well priced.
On the other hand if you crave a noisy CPU cooler I can suggest Thermaltake as a good place to go