Whenever you want to figure out what a particular song or piece of music's tempo is, just load up the program, and hit the space bar to the beat - it's that simple. It takes it approx 10 hits before it will be close, and 20 hits it's at it's sweetspot. It displays both the estimated BPM, as well as the delay (in milliseconds) of the last space hit you made. It's almost like a game; see how accurately you can do tempos! (please note, if you do follow the previous suggestion, you have way too much free time! hehe).
Just a note, this used to be called Metro, but in an effort to confuse and amaze users, I renamed it to TapTempo; primarily because I'm going to make a metronome, and it would make more sense to call this TapTempo than metro, considering this new development.
Special thanks to Rony Brack for suggesting this handy little program!