Tactile Bump Sensors
These are mechanical touch sensors that are used to detect environment. They are used when you need to stop the bot instantaneously.
They are still used in industries with variety of innovations. But in field of hobby robotics you will rarely like to use them as you have IRs, Sonar, etc but these sensors should be used in several numbers to scan the environment. At advance level ( in moon rovers, intelligent ground vehicle, etc) to detect the obstacles robots use laser range finders as they scan and plot a map of obstacles.
The other two types of switches are the magnetic reed switch and the membrane switch, which is much like a long button actuated switch.