Well, the board favorite seems to be the Garmin GPS V. It's a nice mixture of units, offering street driving navigation, and good portable use as well. Batteries for me tend to last about 12 hours with little backlight usage. Memory wise, it is not expandable, but can hold enough for a decent sized area. Mine currently has all of southern Colorado, plus the area across Texas to Dallas, then also Austin. This includes all the local attractions.