I suggest the teratec deep water line of air pumps (tetra whisper AP 150 or 300 model). 150 has one outlet/ 300 has 2 outlets. Quiet, powerfull, dependable, and affordable. The whisper 100 is hit or miss, but i've never had a "lemon" on the deep water series. Lifetime guarantee and when the diaphram's wear out (takes a WHILE) they are easily fixable. They are made to last, not like the regular whisper air pumps.
The regular whisper air pumps are great in the smaller sizes, but I wouldn't buy the 100 model (check out all the negative reviews on amazon). When the regular ones break it is more cost effective just to buy another one than to fix the stupid thing. That should tell you alot about the pump. If you do get the whisper 100 be sure not to restrict the flow of air in anyway! You will blow the diaphrams.
If you want something even better (yet slightly louder) get a piston powered pump. Diaphram pumps by design will eventually blow out their diaphrams.