I have been rather happy with my Coralife Luft Pump;
Coralife Luft Pump
It is rather quit and plenty powerful. If you look you will notice in the picture that there is a little "tab" with a hole in it on the side of the pump. That is so the pump can be suspended from something, an elastic cord works best, and that way there is no seconday vibrations from whatever the pump is on.
A lot of pumps have that little hanging thing on them, so at least look for that on whatever you buy.
Hanging the pump so it isn't in contact with anything is the best way to quit them down.
Hey! I just noticed that the site that coralbandit linked has the luft pump for less $$$.
nice to know.