Harry's Lap Timer Pro HD on the iPhone 4. Device is jailbroken, BT Stack GPS is installed to allow me to connect the phone to an external GPS bluetooth receiver and Harry's Lap Timer Pro pulls all the data from GPS. As well as the video overlay showing track layout and G-Force as well as lap timing.
The pictures above were exports from the software on the phone, one just a PDF which i captured an image from, and the other was a KML file which can be imported into Google Earth.