The BodyMedia Fit Link (limited availability on Amazon) isn't as sleekly designed as the other trackers, but it has staying power for two reasons: it's simple, and it works. Wear the band on your upper arm throughout the day to track calories burned, exercise intensity, steps taken, and sleep quality. You can also keep track of everything you're eating using the online weight management system. At the end of the day, upload your activity stats to see if you burned more calories than consumed. One big downside of this tracker is that after a free six-month membership, a $7-per-month subscription is required to access the data it collects. The BodyMedia syncs wirelessly with smartphones and also plugs into your Mac or PC to download and view data. BodyMedia was recently acquired by Jawbone, so expect its technology to pop up on the company's sleeker design.