I avoid Noble Knight like the plague, but I've had the best luck with ordering from Northstar in the UK. They ship fast and reasonably priced...and often at less than I can find them in the U.S.
I have turned to a lot of Warlord bases for my 40mm/50mm needs as they're better priced, but still use Renedra for stuff like 30mm circles, etc.
PS: If you're looking for 20mm squares, let me know. I've got a bunch of those spare from all the various kits.