Everything else is working and the power mirrors just seem to stop working one day?.
In that case, my first guesses would be fuse, or the switch.
I'd be a little surprised if the mirrors had a dedicated fuse, but I'd be even more surprised if they had a dedicated fuse AND it was located somewhere other than the standard fusebox. Take a look at the ones you have in there, then look to pulling the switch and putting a volt meter on it to see if any wires have power. If so, you're down to the switch itself being bad, or else a bad ground somewhere.