Here is a small battery powered amp I built. Runs on a 9v battery, has gain and volume controls, and puts out 1/2 watt of power. This amp is built in head form, and you must plug it into a cab of some sort, or headphones using a mono to stereo plug. Has a mini-toggle for power, an indicator LED, and has 1/4 input and output jack.

Cleans sound great. Responds to pick attack very well. Overdrive is similar to a Big Muff. Its not super high gain, think AC/DC or Black Sabbath. Takes pedals very well.

A sound clip is available here. The amp in this video is built into a different enclosure, but it is the same circuit - http://www.youtube.com/watch?v=2hKX8L5LFks

$45 Shipped in the US, and $45 + shipping outside of US.