Wouldn't it be nice to be able to (instantly) recognize intervals when a song is played on the radio? If you have been playing music for years, it's probably easy but for the rest of us, mortals, it might be a tad difficult.
A good way to recognize intervals is to match what you hear with the beginning of a well-known song. If you have a browser (who doesn't?), there's this free web application that enables you to play an interval and find the matching song. Now, even if you ace the tests, it doesn't mean that you'll be able to play anything by ear but you'll probably be one step closer.
The web site where you can find this neat little web app is:
Free Online Ear Training
It's a nice little flash application which I really wish I had written. Of course, I know next to zero about flash, so that might have been a tad difficult. Below are a couple of videos that explain the finer points of this fine application.