I assume some of you guys know about this stuff but I've found it to the best sandpaper I've used to date. You can buy it elsewhere but here is a link at Beall and they have a lot of different grits. http://www.bealltool.com/products/other/sandpaper.php
It's just really great stuff and lasts forever. The backing is super durable. I should get a new supply in tomorrow.