Simple, but effective!
This easy-to-build gripper kit can pick up a half-pound steak. Put your fingers between the innocent-looking jaws of the gripper, activate the servo (not included), and you'll feel some real pain! Or better yet, don't and just take my word for it. The grip of this gripper is substantial. (You may recognize the gripper as a plastic woodworking clamp; hence its ready ability to put a squeeze on things.)
The gripper kit works with most any standard-size R/C servo. One is required. The gripper kit has been tested with low-end ($12-14) Futaba, Cirrus, and Hitec servos.
See also the wrist kit.
Available as gripper only, gripper/wrist combo, or gripper/wrist combo with four servos.