I have designed (with some great help and input from the guys at
Dutchforce.com and
DIYAudio.com) a simple guitar headphone amp with an mP3 player input. The MP3 input is stereo and the mono guitar input is split to both channels. Below is the preliminary schematic. I have bread-boarded it so I know it works. I will be making a SMD PCB and possibly a through hole version. I will post those as they are completed. It will be designed to fit in
this enclosure from Radio Shack.

Here are the eagle files:
Attachment:
schematic.sch
Attachment:
schematic.brd
Here is the schematic: