After many years as a happy clipless user, I experimented with a set of the MKS pedals that Rivendell sells as the Grip King (I think they are actually the MKS Lambda?).

I had a lot of fun last summer commuting in tennis shoes. I loved the ability to jump off and on the bike with no cleats clicking at all (I had used SPD's prior to that). In the winter, though, I switched back to SPD's because I have a great pair of SPD waterproof cyclocross boots, and I couldn't find great waterproof shoes otherwise to wear on a bike that didn't slip around.

Now that it's spring again I went back to the platforms but didn't love them. I tried a couple of other things, but am back to SPD pedals again.