As part of a larger project I've started building some virtual parts for simavr. It's turned out to be a real pleasure to use and i'd highly recommend it. Great job BusError!
Here you see an identical firmware running on both the physical device and in simavr. Aside from the fact that simavr runs about 10 times faster than the actual hardware the results are identical. The demo goes through the routine of testing the driver functionality. This includes things like setting the contrast, inverting the display, writing to the buffer and changing the orientation.
Currently the virtual part has only been tested with this driver. If you're using some of the more obscure hardware functionality you may need to extend it. The same goes if you're using the parallel or I2C interfaces.