I work at a very large hospital and I've been hitting the box and bubble wrap jackpot there. They always get a ton of deliveries and have all sizes of boxes just sitting in the shipping/receiving area waiting to be thrown out. As an added bonus I found some top notch bubble wrap they were throwing out. I mean top of the line stuff, not the type you would get at a dollar store or something.
I guess the point of this post is if you're downsizing by selling a lot of things on ebay (like I am) or just need free boxes and bubble wrap, check your local hospital shipping and receiving area. Might be called "central sterile" also. If you have a friend who works in a hospital, ask them to keep their eyes peeled.
Not much in the way of packing peanuts, but you can get those on ebay for a solid price.
Hope this helps someone.