jsPDF is an open-source library for generating PDF documents using nothing but Javascript. You can use it in a Firefox extension, in Server Side Javascript and with Data URIs in some browsers.
At the moment, it only does text. Client-side demo works best in Safari or iPhone Safari. Also works Firefox 3 on Windows and Opera. IE support on the way.
Demo: http://jspdf.googlecode.com/svn/trunk/examples/basic.htm
License: MIT License
Very good, ;D