Shimano SPD (not SPD-SL or three-bolt) uses two different models of two-bolt cleats

SH51 - unidirectional release

SH56 - multidirectional release

It seems to me that the SH56 has more float. These cleats are designed to be recessed into the shoe's tread blocks, which facilitates walking orders of magnitude more so than "road cleats."

These are mostly seen with MTB shoes/pedals, but there are a few road oriented pedals with the A600 being Ultegra level. A530s are a great choice dual sided SPD urban/commuting pedal. There are a range of commuter/road SPD shoes out there, from flexible and comfortable to stiff as a stone rooster.

This is not a general axiom, but the difference in pedaling efficiency between my toe-clip set up (Nike Free w/ Christophe clips on MKS platforms) is worlds behind my current setup (Northwave Jet365s with SH51 cleats on A600s). I plan to keep the current setup throughout the year.