OBD GPS Logger has an OBD II Simulator in the package. The simulator has grown into a very powerful standalone tool, and as such I'm adding this thread as a separate place to make mention of it.
obdsim is an ELM327 and OBDII simulator, that uses plugins for actual data generation. This means that you can use it for all sorts of things other than just developing OBDII software [eg, you can use it with a Fusion Brain to use OBDII software of choice with your pre-OBDII car].
I have created a page just for OBDSim, where some of its features are clarified and detailed. Please visit that page for more information.