i have found a great new source - AmazingPets.com makes a quilted pad that is really absorbent. i believe it is $25 for 100 of these pads and free s&h in the ny/nj/ct area. they will even send you a free sample to try.
i was using the arm&hammer ones (from target) but had to change the pad a lot more often so it was costing me lots of $$$.