If you want to go with the reference standard I suggest the Garmin GPSMap 60CSX. It is slightly older technology but it is proven technology, occasionally you will even see pics of soldiers who are deployed with them strapped on their gear. It is a tough dependable unit.
You will have to buy topo software for it and it isn't cheap. Garmin now offers 24k topos for every state. The maps generally run $100 msrp for two state bundles.
I bought the above mentioned (Millcreek) Magellan Triton 500 just recently for three reasons. I received an employee discount, it was on sale and I own a lot of National Geographic TOPO! disks for areas I regularly backpack. The Triton series allows you to upload the USGS maps from TOPO! right into the handheld unit. This also includes any information (waypoints, routes etc...) you've added on your PC. I saved a lot of money not having to buy software.
This is my first GPS and I'm reasonably satisfied so far. The Vista HCX was the frontrunner before I realized how cheaply I could get into the Triton.