Another avenue to consider is --- if you might be in the market for a new cell phone --- to get one with a built-in GPS receiver. Then you buy software for whatever platform your phone supports (for example, Windows Mobile) that uses the built-in GPS receiver to do various things.
On my cell phone I have normal "driving on the roads" type of GPS software, but also a couple of topographical applications. As long as you get a phone that has a true receiver built in (doesn't have to be in range of cell towers for the location functionality to work), and it has a SiRF Star III chipset (or whatever comes after), should be fine.
One possible downside is that on an extended trip cell phones all seem to have proprietary batteries, whereas your typical standalone GPS uses standard battery types. So if you go the phone route, I'd look for one that has a replaceable battery, so you can bring one or more extra batteries along on longer trips.
Another downside is that this approach might be ultimately more money (possibly a lot more, depending on your choices), plus some more complexity in finding the right topo app(s) that do what you want, getting them installed and learning to use them.
I nevertheless think this approach will get to be more common over time; I think it's Nokia in Europe that's in particular pushing GPS technology into all their phones, and true GPS receivers becomes sufficiently common in cell phones, it will seem silly to carry a GPS enabled cell phone into the woods and also carry a standalone GPS. Ditto cameras at some point, at least for a subset of of us in the "just point and shoot" camp.