One of my favorites would have to be 2056's manipulator/ball gatherer. It was used in unexpected ways when they would shove it under the bridge to aid the balance.
Some people have mentioned 1730's passive manipulator. For those unfamiliar:
http://youtu.be/g_7ljqbIdi8?t=15s
I like the idea behind this design. I haven't seen anything like it other than theirs but if someone has go ahead and bring it up. With video/pictures