Fontsnatcher - Fontsnatcher helps you in identifying, testing and discovering new fonts and typefaces being used on the internet.
What Font Is - Find any font from any image (commercial or free)
Linotype - Linotype: Fonts for Desktop, Web & More
Google Fonts - Making the web more beautiful, fast, and open through great typography
Find my Font - Identify any free or commercial font with your camera!
Fonts Ninja - Try fonts discovered on websites in any design software