Google added a “preview option” to Google Font Directory, that let you edit sample text, change text size and spacing, capitalize the text, add underlines and shadows, before embedding fonts code. “Google Font Directory lets you browse all fonts available via Google Font API. Clicking “Toggle controls” in upper right corner provide distractions free font preview. Fonts in the directory are available under an open source license and are served by Google servers,” explains Google.
Previewer will generate corresponding CSS code, so you can just copy & paste o to start using the font on your website/blog.
More Info: Font previewer