I think you also have to figure out how much you're going to need it. If a lot, I suggest one of the fancy ones that go for over $500. There are many to choose from.
If you're like me and you only need it on occassion but also want the portability (no hand held though or at least it would be akward), I like the i3 by Garmin. It's easy to use, sub $300 six months ago, and I can load all the Western coast of the U.S. on the card it came with. Negatives are no touch screen. Here's a pic:
