I’m not sure if I’d personally call this a robotic pen but it does have the cool factor of a really smooth but slow opening cassette deck (remember those).
Squeeze the button and – in a curiously slow motion which is much of the charm – the pen mechanism unfolds, presenting you with a full sized biro. When you have finished, simply fold the pen up again.
There is a video of it in action which since my recent problematic Vista upgrade I am unable to watch (or play any sound to that matter).
You can get the “some what robotic pen” from Grand Illusions for £3.95 (~$8).
Al, I’ve got one of this (a giveaway from Adobe at the time). It’s lots of fun and the damped spring mechanism surely surprises.