FontForge - Free (libre) font editor for Windows, Mac OS X and GNU+Linux
Scanahand - Scanahand makes it easy to create Windows Truetype fonts from your handwriting.
BirdFont - Birdfont is a free font editor which lets you create vector graphics and export TTF, OTF, EOT and...
My Script Font - Make a font with your own handwriting
Glyphs - Make everything from dingbat webfonts to full-fledged text typefaces in the most Mac-like font...
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!