Zefal mini toe clips are what I would use if I were in your shoes. I used them for a long time and they provide much of the functionality of clipless but you can wear any shoes with them. Power Grips work too, but I could never quite adapt to the feeling of the strap over the shoe. I'm using SPD and mountain shoe clipless now, and they're better than the Zefals, but for casual riding the Zefals should be fine.