www.fontsquirrel.com/ – dubs itself the “best collection of 100% free commercial use fonts”
www.fontspring.com/free – Free fonts from font spring (I am liking Museo Sans. A clean sans-serif font.)
www.google.com/webfonts – Makes using @font-face trivial, so I’ll probably end up using this. (Again, Glegoo and Open Sans look nice to me.)