I usually purchase Simple Solution Economy Puppy Training Pads through Petsmart, see link below. Currently they are having a sale with an additional 20% off. They worked pretty well for me. I just placed an order for 5 boxes of 150 counts. So hopefully that will last me for awhile.
Simple Solution® Economy Puppy Training Pads - Training & Behavior - Dog - PetSmart
I've also ordered pee pads previously from Mednetdirect.com and they are no good. They do not absorb very well.