I have a Garmin, Etrex Legend. It is a small handheld GPS, and has mapping technology. It has map preloaded, and you can buy software to load more specific maps onto it.
It is kind of small, so the maps can be hard to read, especially with the Black and White LCD screen that I have, (there is a color version too)but it is inexpensive, and compact. It is also pretty easy to use, and waterproof. (Up to 2 Meters I think.) It is also relatively inexpensive, at about $150-$180, last time I checked.
I guess the only complaint I have is that the memory is kind of small. I can't put as many maps as I want on it, but that was more of an issue for a long car trip than a smaller boat trip. The Etrex Vista, is similar but has much more memory, (and costs about $100 more I think) It also has some other features that I wasn't too interested in, but might be handy.
Overall I'm pretty happy with it. I hope that helps.