i use a pair of 15* year old shimano SPD shoes for most of the year, and they've done me fine for years. most of my bikes have SPD; the knockabout single speed has flats, and one other has flat/SPD combos.
the shoes have reasonbly rigid soles, they're more at the road end of things.
*just checked - 18 years old. reason i know is that they were bought during the euro/punt changeover.