I figured I'd share my awesome find just in case this isn't already common knowledge. . . even if it is, I still think it's awesome.
"The Mat" by Sleep Innovations
is the best dog crate mat I've ever seen. I found one at costco for less than $10 and had to try it. Mine looks a little bit different than theirs, but it's the 24x36" and fits perfectly in the crate. It's soft, cushy memory foam with a fuzzy microfiber top that you can probably wipe pet hair off of. The bottom has a rubber backing so that it grips the crate and won't slide around, and it's so thick Middie can't dig it up like he does with blankets.
It was cheaper than a typical crate mat because it's designed for the bathroom, is machine-washable, and way more cushiony - and is just the right size for a medium-size dog crate!