The Firebird Trans-am has about the most options that I've seen;
- There are 3 options for the front, which all have different front bumpers, side skirts and rear bumpers. One of these also completely changes the front lights.
- Three different options for the roof panels
- Numerous rear wing options. I also think you can change the back window to be covered in one of the above options.
The El Camino is another car that can be drastically changed, you can change it into a pick up truck, a flat bed or station wagon (well covering the rear with bodywork anyhow).
You should take a look at this thread if you haven't already.
