The MIT licence
The Aleister Crowley Twitter summary is "Do what Thou wilt (provided ye give me credit)".
You can easily find the exact form of the MIT licence, so I'll talk about what the licence is good for.
It's a permissive licence, which means that other people can easily use your code. In particular, they can use your code to make money. The licence obligation on the part of the user is simply to include your copyright notice in all copies or substantial parts of their software.
It's the licence you'd use to ensure the maximum takeup of your software, when you don't care that someone else could use your software to build something and not share their innovations.