[Gigakaiser]

Gyroscope - This will make your autonomous routines 100000x more accurate. Your robot will be able to carry out quick and accurate turns despite drivetrain inconsistencies and battery voltage. It may also be used to keep a certain heading whille driving in a line.

Any sensor for line following (dependant on field of course) - Using a line-following technique is one of the simplest ways to achieve a consistent autonomous routine.
-My team has used these sensors for arm limits as well.

Encoder - Besides autonomous consistency, encoders open up proportional control (arm locking & arm presets) and digital limits.

Potentiometer - Similar to encoders, yet absolute. Encoders will read "0" on startup, while potentiometers will always read values from their current position. Potentiometers have physical limits as well. (not for drivetrain)

Dipswitch - Dipswitches on a robot may be used to set autonomous routines, delays, and other robot settings. Your team may have these capabilities built into its dashboard.

Kinect - This was the most useful sensor my team has ever used, but implementing it on the robot was not easy. With the kinect you are given a grid of depth values - tracking game pieces, scoring zones, etc. are all possible with this sensor.