HiTechnic is releasing their servo driver module for Lego Mindstorms NXT as a stand alone product. It is the same one that's in the high-priced FTC competition kit, and is similar to the prototype that I used in the Lego UAV. Can control up to six servos and/or DC motors, and you can daisychain them for more. $79.

Unfortunately it doesn't have the RC-in multiplexer feature that the prototype had, so you can't just connect your RC receiver to it and use it to switch between RC and autopilot control. For that you'll need a separate failsafe/multiplexer, like this one or Jordi's DIY one (code here).