The program rviz is one of the many tools shipped with the latest ROS release. The documentation looks pretty detailed. I wish there was a tutorial on setting up the camera data overlay with laser data, because that looks great.
Gazebo seems to be constantly improving and can be integrated with ROS or Player/Stage.
LabVIEW seems pretty popular for the blocks and wires programming interface.
MATLAB. I still have not managed to get the Simulink Real-Time Workshop Embedded Coder working. Maybe one day I'll have enough time.