Mounted on the windshield, the GPS equipped unit captures a number of criteria that are useful to the beginning slide enthusiast, with the grip level, slip angle and speed all stored on an SD memory card for future reference. Additionally, the Driftbox will also measure 0 to 60 times, track lap times and give exact speeds (if, for some reason, your 240's speedo is busted after the SR20 swap).
Car and Driver wrote up a review of the Driftbox and measured its accuracy with their own $10k VBOX, a device they use to record all aspects of vehicle performance. After testing the Driftbox along side their own data logger, they found it to be just as accurate as its expensive counterpart.
$750 buys you the Driftbox and all the required mounting equipment and if the whole street racer theme is a turnoff, the G-Tech Pro is another option for gathering performance data from your own ride.