A battery grip is available for most prosumer dSLRs. It fits under the camera with an extended handle and holds two batteries. It provides additional shooting time/exposures and allows for easier vertical shutter releases as most grips have an additional shutter release button for verticals and and a vertical exposure adjustment wheel.
Grips are a bit more comfy, help balance out the camera when shooting with long lenses and they provide a resting spot for the pinky, which would other wise just be sorta hanging out in space.