Microsoft Font Maker - Use your pen to create a custom font based on the nuances of your own handwriting.
FontForge - Free (libre) font editor for Windows, Mac OS X and GNU+Linux
YourFonts.com - YourFonts is an online font generator that turns your handwriting into a font that you can use in every program that you own. 500,000+ fonts already made!
My Script Font - Make a font with your own handwriting
BirdFont - Birdfont is a free font editor which lets you create vector graphics and export TTF, OTF, EOT and...
Fontifier - Fontifier lets you use your own handwriting for the text you write on your computer.