Mechs are a quite probable Military Unit. What comes to mind with a Mech is the things from the Mechassualt Games and etc.. Bipedal, with Fusion-reactors.
Those are a little far-fetched for for now. But Larger walker type tanks could be made, fully armored running of Hydrogen Energy Cells, with a Array of weaponry like Homing missiles, machine guns and quite possibly even Laser Weapons.