I picked up a few of these at WalMart and they work great. The one's I picked up are about 12x16, so they'll be good when I get my enlarger finished and start printing 11x14. I've been looking for something that'll be good for 16x20, but so far the only things I've found have been too deep.
I do have standard 8x10 trays, but I find myself using them much less often than the cheap WalMart trays. I have set aside one of the cheap trays for Selenium toning...I figure that I can afford to replace it if it gets too messed up. It's already pretty well permanently stained, but rinsing thoroughly with hot water gets rid of any lingering odors.