There is a set over on flickr with a batch of geeky tattoos(link) and I while I was going through them I was thinking about what kind of tattoo I would want as a computer engineer.  This is what I came up with:

1. Ohm’s Law
2. A balanced binary tree
3. A transistor/resistor/capacitor/voltage source circuit symbol
4. A short SPICE file
5. A listing of the first X prime numbers.

Any other suggestions?