Get Panaflo case fans. One of the most quiet and they push a lot of air too.
PCMods has them @ reasonable prices. Can get a 92MM fan for $10.99.
Do a search in the forums and see how many people like/want Panaflo case fans. Doubtful you will find anyone that dislikes them.
If you buy from PCMods, be sure to buy a 4 Pin tail (same socket that hooks to your hard drive/cdrom etc...). Don't want to hook a larger fan to your motherboard, it'll burn it out. Very easy to switch out, like plugging a power connector onto your floppy drive.