I like my Wellgo pedals that came off my mountain bike. It's got a big platform that's grippy. I transferred them to my commuter.

If you're looking for a two in one pedal, you can get spd with the platform attachment. I know Performancebike makes a "campus" pedal which is flat on side, and spd on the other. I've ridden on look style pedals in flip flops. It works fine if you're careful, but if it's rainy or wet they get slick.