We've been asked for awhile now what motors or servos we recommend for using with our Crazy Circuits system. We've so far been using some laser cut adaptors that we designed that allows standard 9G sized servos (super common and easy to use) to work in any LEGO compatible environment. They work pretty well, but we were never super thrilled about them as they lacked a certain 'ease of use'.
A friend of ours at BrickStuff.com sent us a couple of these GeekServos for testing this Summer and we fell in love. They're pretty much just standard plastic geared 9G Servos in a custom LEGO Compatible plastic mold with a LEGO Axel instead of a servo horn. There are female LEGO receptors on the bottom and arms, male studs on top of the arms, and even a couple of holes for LEGO axel. The only downside is that the often advertised '360 degree GeekServo' is actually just a two pin motor, not a 3 pin continuous rotation servo. Still, it does give us a simple motor to use with Crazy Circuits.
We're now officially carrying both versions on our website. The gray LEGO Compatible 270 Degree Servo and the red LEGO Compatible Motor version. Since there is no easy way to plug the two pin red Motor version into our system we're including a custom 2 pin Crazy Circuits component with every order. We do recommend using a 2AA or 2AAA power supply as the red Motor will quickly drain a CR2032 battery in minutes.