check this out:

http://www.minidisc.org/headbanger.html#noisebuster

Very technical, tells you exactly what to do to build your own headphone amp. I'm definitely going to build one. Doesn't cost much at all and looks like a lot of fun to build. The rewards should be great too. I don't want to pay $200-300 for a decent headphone amp, so I did a search and came up with this. For $20, you can't go wrong