Air Free tires

http://www.airfreetires.com/shopping...trial-622.aspx

Wal-mart used to sell some hard foam bicycle tubes but I can't find them anymore. I guess Slime and Stan's sealants have replaced that.

Some company was working on some semi-solid tires to be used in Africa. I remember a picture of one with thorns stuck through it in several spots but the bike was still rideable.