Okay, I bought the PD-M530's... they're the cheapest ones ($30-50, depending where you buy):
PD-M530 - PEDALS - CYCLING FOOTWEAR AND PEDALS - LIFESTYLE GEAR - SHIMANO

The next level up in this line are the PD-M785's... they're lighter, tougher, and cooler looking:
PD-M785 - PEDALS - CYCLING FOOTWEAR AND PEDALS - LIFESTYLE GEAR - SHIMANO

The top of the line are the PD-M985's... out of my price range, but if you have the bucks:
PD-M985 - PEDALS - CYCLING FOOTWEAR AND PEDALS - LIFESTYLE GEAR - SHIMANO

All of these come with the SH-51 cleats, which are single-direction (i.e., you need to twist your heel OUT to release).

Shimano also sells the Click'R line (which are dual sided and have built-in reflectors). These come with SH-56 cleats, which are multi-directional (i.e., twist your heel in or out, yank back, or even jerk up). The whole idea of the Click'R series is to be the MOST FORGIVING clip-in system. Some people find it TOO forgiving (meaning you release when you don't want to).
Here's the mid-line Click'R pedal in case you think it's "right for you":
PD-T420 - PEDALS - CYCLING FOOTWEAR AND PEDALS - LIFESTYLE GEAR - SHIMANO

Personally, I find the M530's easy to get in and out of (of course, I have the tension set at the LOWEST POSSIBLE SETTING, which I would suggest all new user try... remember to adjust ALL FOUR tension bolts... both sides of both pedals).