Although they are diaphram pumps, you might look at the Dolphin air pumps. They are put out by Won Brothers. I ordered a Dolphin 3 for a maintenance customer and am very impressed with it. You can't hear it run and, on it's lowest setting, it's driving two 12" long airstones in a 55gal tank.
Life is not measured by the number of breaths we take, but by the moments that take our breath away.