I think what you are looking for is a servo. At least, that's what it's called in the hobby, officially it's a servomotor. Each unit consists of a motor, gears, a sensor to measure the position of the output shaft, and a comparator circuit. The electronics compares the requested angle to the actual angle, and drives the motor as required to minimise the difference.
They're commonly used to control the steering for RC cars and boats, or the control surfaces in RC planes. They are specified by their movement speed and torque. Better servos have ball bearings on output shaft, and you can get metal gears for tough applications.
You might want to look at the servos used for retractable landing gear on RC planes. These servos only have two positions, and are generally geared a bit lower for extra torque.
Servos generally run at 4-6v and are controlled by a pulse width modulated signal from an RC receiver. Alternately you can buy a 'servo tester' for about $5 to generate this signal, or it's easy to generate from an Arduino.