I use "Rackspace Cloud Files" service as CDN, which provides a nice API for many CDN-related automation tasks.
How do I integrate Drupal with Rackspace Cloud Files without manually copying static files to the CDN?
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You can automate the delivery of content files with the File Conveyor mode, this module integrates with the File Conveyor daemon. This allows for much more advanced setups: files can be processed (e.g. optimize images like smush.it, minify CSS with YUI Compressor, minify JS with YUI compressor or Google Closure Compiler, before they are synced and your CDN doesn't have to support Origin Pull, any push method is fine (supported transfer protocols: FTP, Amazon S3, Rackspace CloudFiles). File Conveyor is flexible enough to be used with any CDN, thus it enables you to avoid vendor lock-in.
Use the Cloud Files module. You can set the file system to Rackspace Cloud Files so that files uploaded to Drupal will be stored and delivered from Rackspace Cloud Files CDN directly (no copying).