I use VP VX Race pedals with Giro Republic road shoes with a walkable sole. I bought 3 sets of pedals when someone on ebay was selling them for $25. I only use them on my road bikes now, all my flat sole road shoes and pedals are in the closet forever. The VP's have a little extended platform on each side that does a nice job of giving extra support. I just had to trim the bottoms of the shoes a little because it was hard to clip in.
If you have SPD's and want to ride with regular shoes on occasion you don't need to buy platform pedals. Problem Solvers has a clip in platform that..... solves the problem. You bolt a cleat to them and snap them on. I tried some one sided Shimano platform's like someone posted above and when I was clipped in the sole of my MTB shoe hardly even made contact with it, it was a waste.
