I use a garmin emap, which is probably not sold anymore and its an old product even if it is. Look for a handheld black and white garmin or magellan unit with a built in basemap of US highways and exits. PC connectivity is a plus but unnecessary for most uses. I've only used mine for "ok, where the ^%#$ are we?!?" and "I know the dang highway is right around here, now where is it, how do I get to it, and wheres the nearest entrance ramp?". The compass and altimeter are modestly useful at times to get general bearings and see if you're above or below freeze-lines and need to watch for black ice.
Check here
http://www.cycoactive.com/gps/gps_compare.html
For a comparison...looks like the garmin etrex legend or vista is what you want...I've seen them around for $99-150 a pop. The $99 price was a circuit city clearance item. Amazons prices aint too bad. You might want to go into staples or a circuit city and poke at them to make sure you like how the screen looks.
Note that they need line of sight to lock the satellites, so in the middle of an RV or inside a building, even under very heavy tree canopies you can lose the lock.
Gotchas: the downloadable detail maps are expensive, often out of date or surveyed wrong so things are in the wrong places. "autorouting" is worthless...my last autorouter tried to take me through an active trainyard to get to a street. If you're going to want to download detailed maps into the unit, find one that takes a standard compact flash...garmins proprietary flash is 10x the cost of regular flash. If you're one of the super detail types, you can work out routes and stopping points on a big map on your pc and then download the routes, waypoints and points of interest to the gps for later use in the car.
If its something you think you're going to use all the time, and you want a more prominent/permanent mount, a larger color unit IS easier to see and use but you're going to have to pony up $300+ for one, probably closer to $450 for anything decent. The small handhelds are pretty handy though, I've taken my emap on boats during ocean sailing trips, out on lakes, and on walks through the state forests. Pretty much paid for itself 10x over when we were sailing on the SF bay and the fog rolled in and we didnt know where the shoreline was.
A few years ago when my dad wanted to drive from New England to California when he was moving here, I sent him a Garmin Colormap pre-programmed with the route he needed to take to get here from there, and a countdown showing the miles left to go to get to my house. All he had to do was turn it on and drop it on the dashboard. He said it saved his bacon a couple of times.
Radar detectors are worthless these days. I spent many years with expensive dashboard ones and when driving extensively in connecticut where they're illegal, with a hidden remote one run from the cars grill into a receiver in my glove compartment. Saved me a lot of tickets then.
While radar detectors are a lot better now, radar has simply outpaced them. Instant on, lidar, short pulse Ka and better trained cops have gotten things to the point where they're going to have you before you get an alert. Further, having a detector in sight makes you not only a theft target, but a "nuisance ticket" target. The average person breaks 6-15 obscure and not so obscure motor vehicle laws per day. Seeing a detector ticks off the cop sitting at the light next to you, and theres a good chance you'll get harassed. I used to get tickets for "improper starting, stopping or turning", license plate obstruction (a dealers plate frame), operator visibility obstruction (a map book sitting on the dashboard), etc. Then I wised up. Drive within 10mph of the speed limit, watch for anyone weaving up through traffic behind you, or ideally find some dick in a Porsche with a radar detector thats going 80 and keep him barely in view ahead of you. When he gets pulled over and written up, you drive right by and wave.
There are a hundred people who will line up to tell you their fancy and expensive detector has saved them dozens of tickets. I can ante up a thousand cops that will tell you they've nabbed people every day with every model detector on the market.
In my old stomping grounds, there was a CHP that had a nice routine...he sat right on the other side of a sharp berm in the highway with the low power Ka pointed down at the road. You went over the berm and he was about 40 feet away and you hit his beam just as he came into view...and neither of my two very good detectors even uttered a peep until I saw the police car. When I drove across country with my Escort, I had a dozen highway patrollmen hit me with the instant on out on open roads when they were coming in the other direction.