We looked all over the place for robotic arm kits that were not too expensive, but allowed a good range of motion and several different joints.  We finally decided on the Robotic Arm Trainer 007 from OWI Incorporated.  This arm kit was relatively easy to assemble (~3 hours) and was quite fun to construct!  Here is what things looked like before we began:

 The arm has five degrees of freedom and five 6V motors for each piece: the base, the shoulder, the elbow, the wrist, and the gripper.    

The arm kit came with an el-cheapo control box, but we needed a more flexible circuit so that we could control the motors via the microcontroller.  So we decided to build an h-bridge circuit with a pulse width modulation trigger and direction signal to control the forward/reverse direction of a single motor, and then we created a train of relays to select/deselect which motors to move.