This little Aluminum Sound Tube MP3 Speaker from ThinkGeek is about the size of the tube inside a roll of toilet paper. It functions as an external speaker for iPods, or you can use it as a standalone MP3 player. ThinkGeek says that the tube delivers a big sound. It has a rechargeable battery that delivers 6-12 hours of playback time. It has a built-in MP3 player and comes with a 2 GB Micro SD card (supports up to 8 GB card), an armband/belt holder, and a clip to mount it to your bicycle handlebars. The Aluminum Sound Tube MP3 Speaker is $39.99.