I love my Shimano PD-M324. They have clips on one side and are flat on the other.
Most of the time I clip in. I find that they are weighted so that it's easy to get the clips up when I want them.
In heavy city riding though, I'll unclip and go with the flat side.
The best thing though is that if you prefer to stay clipped but need to put a foot down at an intersection, when you need to get a fast start you can jam on the flat side to get through the intersection and then re-clip. I do this 2-3x on each commute (but then I pass a couple dozen intersections).