I have a Skito Endurance pad. Its rounded though and I don't think they make a square one. I love it because I can take the pad/foam out and wash the outside. I don't know how many times I've washed it and it comes out looking brand new every time. Its pretty much the only pad I've used for several years.
My second favorite is an old mac/Cavallo all purpose pad I've had forever.
My husband is a pad junkie but his favorite is a classic equine impact gel contoured pad with wool top
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France