The Google Font Directory lets you browse all the fonts available via the Google Font API. All fonts in the directory are available for use on your website under an open source license and served by Google servers.

View font details to get the code needed to embed the font on your web site. Please also visit our quick start guide and FAQ page. For more help and suggestions, use our moderator page

Also available is a Javascript WebFont Loader co-developed with Typekit. Another step towards beautiful typography on the web.  /via @daringfireball.