Thanks wortelsoft, yeah that's precisely the goal of "minimalduino
"-- a bare bones, mostly single-sided board that is shield-friendly. Install everything or just the ATmega and its cap and reset resistor, whatever you need. Also 5V/3.3V switchable if you want it to be.
I just uploaded version 107 with fatter traces, easier for home etching. It's in a shared Google docs folder
with a 600dpi jpeg of an etch-ready pattern; here's a small version:
The jumper across the ATmega is annoying, but it's not tough to solder an insulated jumper across the bottom or a non-insulated jumper under the IC socket on top (but it may make the socket sit funny on the board).