There are plenty of toy robot arms on the market. If you need one for a serious project, you should give the ViperX 300 Robot Arm a look. It is constructed from 20mm x 40mm extruded aluminum and 3D printed ABS materials. You can 3D print custom grippers to use with the robot.
This robot arm has DYNAMIXEL XM540-W270-R & XM430-W350-R servos for smoother movement and a CM9.04-C open source controller. The ViperX 300 offers 5DOF and 360-degree range rotation. The working payload is 750g.