The whammy bar (also known as a vibrato or tremolo) has been used for many, many years by many famous guitarists. It can be a very expressive and almost emotional tool when used by artists such as John Petrucci and Joe Satriani, but it can also turn the guitar into a beast when placed in the hands of Dimebag Darrell or Steve Vai.
There are several types of bars, the most versatile being the Floyd Rose/Kahler style. It can be pulled up or be depressed towards the body of the guitar. There are also floating tremolos, which can be pulled up or down too, but aren't as capable as a Floyd Rose style bar. Another type of whammy bar is the kind you find on a Fender Stratocaster guitar. I believe those are called synchronized tremolo bridges. They can't be pulled up unless they are modified.
Whammy pedals can mimic the sound of a bar, but can actually change the pitch of your guitar by octaves rather than just semitones. Some famous users include Buckethead and Tom Morello.
Join this group if you use your whammy bar, and you should invite your friends also!