What exactly is a Content Delivery Network (CDN), how does it work, and why would I want to use one for my web site?  Which are the well-known CDNs out there?
CDN - Content Delivery Networks. How do they work and why would I want to use one?
cdn
DefinitionWikipedia says it well:A content delivery network or content  distribution network (CDN) is a system  of computers containing copies of  data, placed at various points in a  network so as to maximize bandwidth  for access to the data from clients  throughout the network. A client  accesses a copy of the data near to  the client, as opposed to all clients  accessing the same central server, so  as to avoid bottleneck near that  server. Content types include web  objects, downloadable objects (media  files, software, documents),  applications, real time media streams,  and other components of internet  delivery (DNS, routes, and database  queries)BenefitsUptimeDownload speedFile mirroringFaster page download perceptionCommon CDNsAmazon CloudFront (in tandem with  Amazon S3) is a CDN that I use and love.Cloud Files by Rackspace Longer list of free and paid CDNs at Wikipedia