Caravan canopies (at Costco i think) or Impact Canopy are probably the best quality.
Spend an extra $100-$200 and get something that will last and can stand up to reasonable winds so you don't frantically run after it down the pits.
The wall-mart one I got for $60 will last this season if I'm lucky at all... crazy winds bent two of the legs and completely demolished my neighbours canopy!
I too would be interested in a good quality canopy. Who stocks them?