Speeding Up Your PHP Web Site
Using a Content Delivery Network
One of the suggestions that tools such as Page Speed and Yslow make is to use a Content Delivery Network (CDN) for serving static content. In effect what this means is that a copy of the content you are trying to serve is stored geographically nearby the user requesting it, in order to fulfill their request more quickly.
When you implement such a solution, users will still access the pages from your web site directly, but assets such as images and movies will be downloaded from the Content Delivery Network.
There are many providers that you can use for your content delivery needs, but as a simple and cost-effective measure you can implement you can use is Amazon S3.
For full instructions on using Amazon S3 with your web site, refer to the PhpRiot article about Zend_Service_Amazon_S3.