I'm new to geocaching, and have been using the Garmin Forerunner 305. It's designed for running (which is why I bought it), but I've discovered that the navigation features on it to be very adequate for geocaching.
Are there other features on other units that really help out a lot? What more do you really need other than an electronic compass pointing you to where you need to go and how far away you are? I'm sure I'm missing plenty here.