I've tabulated that, looked at a stack of schematics, and generally faffed around to come up with this.
www.robgray.com/temp/Arduino-shield-pins-used.xls
If you don't trust an XLS file here's a screen shot
Well I can trust it when I'm not on my computer ;D
I have saved that, looks very nice, just need a way to get that as a nice looking table on a website now. If I get the time, i might see what I can come up with.
But if it's worthwhile I can verify more over time, or maybe others can chip in or the owners of these boards can tell us exactly what pins they use.
Well if we can get some kind of permenant web-based version (not google docs...) then it will definitely be useful to a lot of people.
Mowcius