3. Bushnell ONIX 400

Price: $500

For boaters, the Bushnell ONIX 400 shows standard and nautical measurements. It's unaffected by stormy weather but does a good job predicting it. The handset picks up 178 channels of XM Satellite Radio, including NavWeather, which delivers local reports on a color screen, just like an evening-news forecast. A minor design issue: The exposed metal ports may corrode in salty air.

4. Garmin Rino 530HCx

Price: $536

The Rino includes an altimeter, a speedometer, and a two-way radio with a range of up to 14 miles. Others carrying devices on the frequency show up as blips on the color screen, making it easier to meet fellow skiers mid-mountain. (It also lets you know when to head home; the radio picks up NOAA weather channels.) One caveat: The Rino is bulky.

5. GolfLogix G.P.S.

Price: $350, plus $30 annual subscription

Because hole positions on a golf course often change, GolfLogix (which has hardware made by Garmin) gives measurements to the front, center, and back of a green. A yearly $30 subscription fee lets golfers download an unlimited number of course maps from a library of more than 15,000 worldwide. The cell-phone-size handset can store up to 10 course maps at a time.

Find a Friend

G.P.S. tools for the socially inclined

In addition to sports, G.P.S. receivers are also playing a role in social networking. "About 20 percent of our users choose to be public," says Jason Uechi, co-founder of Mologogo, a G.P.S. application for cell phones that tells your friends—or if you opt to be "public," anyone who visits Mologogo.com—where you are at any moment. At Montclair State University, for $215 a semester, geeks and nongeeks alike can carry Sprint phones equipped with Rave Wireless, a similar, phone-based G.P.S. technology. And endurance athlete Dean Karnazes, who ran 50 marathons in 50 states over 50 days in 2006, uses Bones in Motion, another mobile-phone G.P.S. program, to promote his memoir, Ultramarathon Man. It gives his location to fans and is accurate to within three feet. "People show up at random street corners and run with me," he says.