Shoot, I have some cheapo Wellgo pedals that are SPD on one side and flat on the other. Shimano also makes plastic platforms you can snap into SPD pedals; I even rigged one up with a set of toe clips and straps. Handy when I want to take my commuter bike somewhere where I know I'll be walking a lot at the destination.

These are better alternatives to changing pedals out frequently, as it's probably not good to be unscrewing and screwing on those threads lots of times.

There are also lots of MTB SPD-compatible shoes that recess the cleat well into the shoe tread, and look vaguely like hiking shoes. I even have a pair of (hmm, Lake? I forget) shoes with recessed cleats that are all black leather with a bit of nylon, that pass for casual office shoes.