I will also add a vote of confidence in HDDN. They are part of the NetDNA architecture but have a pay as you use it approach. We use them heavily and have had no problems (not an employee or anything, just an advocate after trying the others). Also, you can consider things like Amazon S3 or EC2 as well. It all depends on the file types and of course, the cost you are willing to absorb to achieve the results you need.
Another option is a Online Video Platform for hosting and management of your content. Here's a list of ones that we've spoken to or are working with: Brightcove Ooyala Kaltura Endavo media The Platform Unicorn Media Castfire
We currently use Amazon Cloudfront exclusively. If you want a simple to use pay as you go solution, they work great. The only downside for us has been the lack of statistics. Amazon only provides virtually unreadable log files. The streaming of videos has been very reliable.