The two available humanoid models that come to my mind are the Nao and Romeo description. These currently offer no gazebo support. Simulating a full body humanoid is a challenging simulation task (at least when not cheating by artificially nailing the standing foot to the floor or using other hacks). As far as I´m aware, there is no solution for gazebo available at the moment, so you either have the option to try it out yourself or wait a little, as Gazebo will likely be significantly improved in this direction in the future for the DARPA robotics challenge.
Another related option would be to have a look at the OpenHRP3 simulator, which works very well for humanoid robot simulation (but has no ROS interface). /edit: As described in the comment below, there is a ROS interface available.