[EricH]

Potentiometers and encoders can tell you distance and angle, depending on how they are used and assumptions that are made.
Limit switches tell you if you have (or better yet, are just about to) hit something.
Ultrasonic sensors do the same thing as limit switches, except that they also tell you how far it is before you hit it. (There are other range-finding sensors but those can cost a pretty penny.)
Light sensors can be useful for line following.
Cameras help you sight on a target.

Care to elaborate on a potential application of said sensors, or is this more of a "We are about to lose money from this year, what should we stock up on?" type of question?