I could spend hours raving about how complex and impressive the science behind query by humming is. Researchers have been trying to develop this for years and I think they've really gotten somewhere with Midomi.
First, let me tell you a bit about what query by humming is. This technology is basically a new version of music search that uses a recording to search through millions of songs. So you just have to attach a microphone to your computer and hum or sing a tune in it. This is then quickly uploaded and run through a massive directory of songs from all languages so you can find out the name of that song that's been stuck in your head for the past week.
Midomi is hands down the most accurate and developed website for this and after I tested it a few times, found that currently its accuracy rate is around 65%. You might think this sucks; and it does. But they are constantly making adjustments and improvements. Plus, every time a new user uploads a recording, they will take "advice" from this to help raise accuracy.
But not only does Midomi do this, it maintains lists of the hottest songs and artists as well as reviews for many things. So this is really your one-stop shop for pretty much all your music needs.