Use a Content Delivery Network in Joomla!
A Content Delivery Network (CDN) is a geographically distributed group of servers which provide fast delivery of Internet content, including HTML pages, javascript files, stylesheets, images, and videos.
CDN for Joomla! is made to work with any CDN system that supports Pull Zones.
Here are some popular CDN providers that will work with CDN for Joomla!