I needed the exact same thing, so I bought a Garmin GPSMAP 76CSx, upgraded from a 76CS I had before. It's sold as a marine unit, but I mostly use it for car navigation and hiking. I've used it for the last few years, and now I don't ever leave the house without it.
Its driving directions and points of interest (gas stations, restaurants, shopping, etc) are as good as any car gps, but it has a smaller screen than most auto units, doesn't have traffic info-based reroute or 3d view, and only beeps rather than giving voice directions. These are the compromises of a handheld unit, but have never been an issue for me.
It comes with a variety of mounting options - I have the permanent car mount, the temporary car mount, and the handlebar mount.
To effectively use handheld units, you must also buy maps to put on them. They come with a base map, but the base map only includes major highways. I purchased navigation maps for North America for driving, 100K-level USA topographic maps for hiking, and Bluechart marine maps of the US western coast for sailing.
The cost for the gps unit plus all the maps is as high or higher than the best auto gps units (which come with built-in US maps). And remember, there are still the other trade-offs for handheld units. But in return, I have a unit that works well for many purposes, has a long (~14 hour) battery life, and is more rugged than auto gps units. With a single 1gb microSD, I carry auto navigation, topo maps, and marine maps for more than the entire southwest US.