There's another much-hyped 70 buck hipster kit coming from "Automatic Labs"...supposed to start shipping iphone version at end of August; Android in the fall. The Bluetooth device has usual CEL interface, but also reminds where you parked, "Crash Alert" calls for help if you are in an accident, evaluates most efficient way to commute, etc. It will also throw a hissy fit when you really giv'er. Might be worth getting just to hear those shrill lamentations every day. https://www.automatic.com

 

I believe the GoPoint BT is the only currently available bluetooth OBD interface that will work with a non jailbroken iDevice.

Which app depends on what you want to do...