There are a few all-terrain wheelchairs on the market today. Here are the ones we've found:
Action Track Chair
Action Track Chair
Action Track Chair Video
X8 Extreme 4X4 Power All-Terrain Wheelchair
X8 Extreme 4x4 Power All-Terrain Wheelchair Video
Bounder All-Terrain Wheelchair
Bounder All-Terrain Wheelchair Video
Nomad All-Terrain Wheelchair
Nomad All-Terrain Wheelchair Video