There are shields in the adafruit and sparkfun libraries that pretty much do that, showing where all the pins are.
Gives you a place to put headers to put pins that could could into a header, or a place to put a header if one had a pin equipped Arduiono.
I've never had much need to plug a populated Arduino onto a board - I just build the Arduino functionality in, for example on this shift register board, where you can clearly see the an Arduino less USB Serial interface chip at the lower left.
(I just got 10 more bare boards in if anyone needs a board with 96 high current sinking pins)
