These work really well with SPDs
http://www.rei.com/product/765129 They're on sale now.
There is a little contact of the cleat, you can hear it on tile or concrete floors, but do not compromise traction at all. They are stiff enough for pedaling but still comfortable to walk in. Nobody will notice you are wearing bike shoes. The next model up from these uses velcro straps if you don't like laces.