I started with the Garmin eTrex yellow and had no problems with it. It is a great simple to use unit, inexpensive, and what I feel would be a good introduction to using a GPS. You can always upgrade later if you want. I now use a Garmin Geko 201, which is almost the same as the eTrex yellow, but has a better signal and is smaller. I didn't want all the whistles and bells, so this is perfect for me.
Hope this helps!