How to Keep Furniture and Appliances from Scratching Your Walls

Scratches in the walls can be frustrating, especially if you have a security deposit on the line.  We have a full-length mirror leaned against a wall in our place, and I'm constantly making sure it hasn't made any scuffs in the drywall!  But what if I told you there was an easy, super-cheap way to protect your walls from your furniture and other free-standing structures?

I use poly foam a lot to absorb sound when I'm recording voice overs at home.  It's only about two bucks per square foot at a hobby shop, and it works pretty darn well.  And I'll have to get some more now that I've discovered this...