Originally Posted by tractorlegs

+1 on this, if you want to stay connected to the pedals while commuting SPD is the way to go. You can get in and out without even thinking about it.

Another (unpopular?) option to think about is platforms - I switched from SPDs to platforms about a year ago and it's pretty nice. You wear whatever shoes you want, you never worry about getting in/out of the pedals, and (in my case anyway) it doesn't slow you down. There's been threads here in Commuting where others say that they feel more secure with clipless and are afraid their feet will slip off of platforms, especially if there's rain or snow - but it's definitely an option that simplifies things for commuters.