Essential OBDII reader: all your data are belong to us!
I did a bunch of digging through specs and compatibility issues. Save yourself a lot of time and just get this - the PLX Devices Kiwi 3 - it'll be the best $100 you spent on getting your car's engine and performance data for use with your track day video.
There are a LOT of wireless OBDII devices out there and some of them will work with your favorite Track Apps like Harry's LapTimer and TrackAddict but *many* of them won't work at all. The added bonus of the Kiwi 3 is that it runs on the latest rev of Bluetooth Low Energy (4.1) and is compatible with Android, iOS, and Windows Mobile (but c'mon, who's using that?).
Options for purchasing:
Get it here on Amazon.
Get it here on eBay: PLX Devices Kiwi 3