I have mtb shoes (Specialized Taho) and Speedplay Frogs which I use on my road bikes. No moving parts and nothing to adjust. Very easy to get in and out of, and I can walk on the cleats just fine. http://www.speedplay.com/index.cfm?fuseaction=home.frog Frog cleats should fit on SPD shoes, too.
Since you already have experience with shoes and clipless systems through spinning, what about taking your shoes and bike down to your LBS and asking them to let you try a few different systems on a trainer?