How about an Antares Martian lander? It can be like Apollo + Mars + the future! You would need an extra docking area somewhere between the HAB and Antares LR. This of course raises questions about the lander itself- where would we put it? We could have a larger HAB module with a slightly different interior- there would be two docks, one for Antares and one for the lander. This would be good, because then you could change the lander for different kinds of missions. You could even dock a large probe if you were just doing a Venus flyby, and you wanted to drop something into the Venusian atmosphere.
Maybe in version 3...