It's often useful to have a short list at hand of common web fonts in use on the web. This page summarizes the most used web fonts across various platforms and operating systems. As you can see, this is a good starting point when it comes to provide fallback mechanisms and practices for backward compatibility for font specification. Fonts like Arial, Helvetica, Georgia and Verdana (and many other) are very hand for creating web pages that degrade gracefully when a specified font is not available on the user's system.