Here is a two-way communication little "remote control" type app. The idea is that the host (the car), sends it's sensor information (all four sensor ports) over to the client (the hand-held remote control) that displays this information. The hand-held remote control, the client, also has buttons that can be used for driving the motors. When these are pushed the values are sent (from the client to the host, this time) up to the car, and in turn drives the motors forward.
Note: a wait was put in here to slow down the constant flow of Bluetooth information. If you have "send" in one direction in a tight loop (constantly sending), it'll block the Bluetooth communication channel and not let the "receive" come through.
1) Video showing it working on two NXTs
2) Screenshot of the host (car) code and client (controller) code
3) Zip file of the code