Here's my choice. Lowrance I-finder. It has a base map of North and South America that shows cities, roads, rails, lakes,and streams. It supports MMC cards and SD cards to 128 M. They sell it in four configurations. One has tons of info on roads, gas stations, hotels and such, One has 70,000 navagation aids for the Great Lakes, the East and West coasts. The basic model is available at Wall Mart for 219.00 right now. You can add the MMC cards as you like. Or they sell it with their map software and the interface for your PC.
They even have an Easy Mode for beginners. I've had a Lowrance GPS unit and an Eagle GPS unit (made by Lowrance), and the only problem with them is that their old units is their need for batteries. They use 4 AA cells, and their new units use 2 AAs.
My two cents.