Beginner Parts Kit Identification Guide
Contributors:
jimblom, 
bboyho
jimblom, bboyho 555 Timer
Closing up the cast of components is this staple of timing circuits.
It's a component whose use is so open-ended that contests are held to see who can conceive of the most useful, complex, and/or artistic use of the thing. With the 555 at the heart of a circuit, and a handful of choice resistors and capacitors, you can create a variety of waveforms that oscillate at frequencies from thousandths to hundreds of thousands of a Hz.
Looking for more examples with the 555? Check out the link below for 555 timer circuits.