A recent NASA TSP (PDF format, free reg. req.) describes a planetary rover concept in which the robot could travel through the air, across solid ground, over liquid oceans, ice, and even snow - all the environments one might encounter on Titan. The trick is giving the robot 2 meter spherical "wheels" filled with helium. The beach-ball wheels also allow the Titan Aerover to survive impacts at up to 50 MPH. For more photos, see the older Space.com article on Aerovers.