Well the newest thing I've come across in recent years is the wide availability and reliability of brush-less DC motors used in the radio control aircraft industry. By utilizing now inexpensive driving electronics using efficient MOSFET switching transistors they can get very impressive performance these days.
So the combination of brush-less speed controllers (work like servo control using PPM command) coupled with newer rare earth magnets in the motors and Li-poly batteries has really advanced the state of the art in electric motor flight that can rival gas powered IC engines.
I'm sure it could be utilized in robot design, however there is a price premium paid for the higher power/total flight weight performance not necessarily needed for robots.
http://www.atlantahobby.com/Store/pc/Motors-Brushless-c371.htm
Lefty