What do your friends have? Magellan or Garmin? Get the same as them as then its easier to trade track files.
Make sure whatever you get has upgradable memory(like an SD card that can be removed). Also a USB connection is nice(my older GPS uses a com port) but I think most of the new ones do anyway. Get the biggest screen you can afford.
Street navigating GPS units do not work for off road use, you need one more geared towards hiking.
Once you get the above figured out, go into GPS Central(
http://www.gpscentral.ca ) on Blackfoot TR by Shaw GMC. Play with a few different models and then decide what you like. GPS is really a hands on thing and you need to actually play with a few to decide what you want.
A run a Magellan that I really like but the next one will probably be a Garmin as my friends all run garmins and swapping files is a pain. Nor looking forward to it though as my Magellan runs perfect whereas they have numerous problems with their Garmins freezing up. Last weekend 2 of them had both their units freeze up at the exact same time. :?