I use the Igloo 5-Gallon round cooler. It's easy to replace the spout with a ball valve and I built a false bottom out of CPVC. I was really nervous about how flimsy the interior of some of the rectangular coolers were because I didn't want something that was going to leech out anything toxic during mashing. The Igloo is BPA free and I haven't had any issues with capacity (even on higher gravity Belgians and Imperials), but if you want more capacity or are running 10-gallon batches Igloo makes a 10-gallon version.