I've been commuting with a pair of Crocs Literide Pacer shoes.....the ones that look like business shoes from above. I put them on one day it was raining and haven't gone back. They're plenty stiff enough and fall nicely into the plastic toe cups I use. They're punched full of holes so I won't be using them in the winter.
I bought them on a whim one day and it turns out they're actually pretty nice.