Using an iPhone app to log your bike rides is nothing new. But the $99 LiveRider kit is the complete package: a shockproof iPhone mount, wireless sensor, and an attractive app for displaying all your ride data in real time.
LiveRider claims to be the first wireless cycling computer, placing a magnetic sensor near the back wheel that measures speed and pedal cadence and beams it to your iPhone or iPod Touch, seated snugly in its frame-attached mount, via a 2.4 GHz wireless receiver plugged in to the device's 30 pin connector. Then, the free LiveRider app gives you real time data on speed, cadence, power output, calories burned, and the rest.
The system also taps into your device's GPS to keep track of where you're going and uses its accelerometer to measure inclination. But the coolest feature, as Wired's Charlie Sorrel points out, is a Chase Rider mode in which you can compete against your previous best times on any given route—yup, just like the ghosts in Mario Kart.