I have the full version of the Torque app ($10) with the PLX bluetooth OBDII connector ($100). I am still learning my way through the program and just recently got my Ram, but has been very helpfull for my Toyota, fixed the cold start problem by showing me a sensor that I had overlooked was bad. Thats another good thing about it, not vehicle specific. Will display and clear error codes and go online and search for information about them. The Torque app has it's own forum also for support. It shows live data and you can customize the gauges between five different customizable screens. It uses the phones accelerometer to give X, Y, and Z axis accelerations. This allows the program to compute horsepower. For the car guys you can even record lap data. It also used the phones GPS for speed and 'follow me' maps. It will compare the GPS speed to the computer speed and tell you the difference. Lots of nifty stuff. I plan on doing a lot more with it and will post back with results.
There is similar apps for Iphone, and I think you can directly hook the Iphone up to the OBDII port and not have to go through bluetooth. There are also wifi connectors available.