A cheap way to get your Libraries from a CDN is the google CDN that offers a wider range of different libraries.
The first advantage of using a CDN is that your static files like images, javascript and css files get delivered from a server near the users access point and the second big advantage is that the content gets delivered from a different domain as your own. Files on different domains can be downloaded by the client (your browser) in parallel to other files from your main domain.