I recently purchased an eTrex Summit. Topo maps are expensive, but if you're computer savvy you can load some on yourself. I can dig up the links if anyone is interested. Unfortunately, I got one of the few models that makes it a pain to load maps on (the ones w/microSD card slots are simplest).
My research narrowed it down to a few key features:
1) Electronic compass. Having it figure out which way you are facing while stationary is impossible without one. Even walking speed they can sometimes have trouble (depending on your speed). This was a must for me.
2) Memory. If I traveled to a lot of different areas this would be important. I generally don't, so the 24 MB that come with the Summit is plenty for maps. Unfortunately, the ability to load those maps wasn't well-advertised. MicroSD slots are simplest, but others also have what's called "mass storage mode", where you plug it in to the USB on your computer and it's drag-and-drop like an external hard drive. The Summit has neither. There may be other options, but I haven't found them, but haven't exhausted my search yet either. The Topo software is easiest, but there are ways to make other maps based on freely available topo information. At any rate, after using it, I'm not sure how useful the topo stuff would be. The screen is pretty small, so the topo lines would be more of a novelty than anything (atleast for me). I'm more interested in marking spots / keeping tracks anyway.
3) Color screen. It might seem like an unnecessary novelty, and maybe it is, but you certainly wouldn't buy a black-and-white TV at this point. I went for color, and I like the screen a lot. I'm sure b/w works fine though.
I've only had mine a month, but haven't lost signal while in the woods yet. All in all i've been happy with it, and can recommend the Summit if the above features are of similar importance to you. The only bad thing is the games it comes with... they're tempting after sitting in a tree for 4+ hours and not seeing an animal. Must... resist... games... ahhhhh!
Oh, and when you buy one, go to Amazon or Newegg and purchase online. You'll save a decent amount of money that way. Actually the Summit has gone up ~$25 since I bought mine... hmmm. Still $30 cheaper on Amazon compared to a popular outdoors store though.