I use an Oregon 300, now discontinued but there are newer versions; with OS 50K map added option (you can buy this at a later date).

I think its a great unit but find sometimes the screen suffers in strong sun light. It's great for paperless geocaching and you can write short logs while out, good for when you do loads of caching in a day. Easy to download and upload from the unit and can hold 2000 geocaches plus waypoints.

Best thing is to go to an Event and see different units cachers have with them and ask what they like and dislike about their GPS.