This is one of those posts that will likely get little attention because you can get much more information from a couple of google searches than any cares to type into a message on here. Try google.com
Some sensors and example applications.
1) Thermocouple - for measuring temperature of say car radiator.
2) Microphone - for speech input to be modulated and broadcast over FM stereo.
3) Strain Gauge - for measuring small weight like a milligram scale.
4) Photodetector - for measuring power and wavelength content of light input.
5) Coil of wire! - Metal detectors, radio frequency pickup sniffers..
6) Pyroelectric - Measuring changes in background IR spectrum.
google some of these for many more example applications that I have not listed.