It is probably hard for people to give you recommendations if you don't give any details about your usage.
But I've used maxcdn[1] before but they seem to have changed their pricing recently, but they do allow you to pay upfront and they do email out cheaper deals about every month for large-ish amounts (5TB and up).
But I've used maxcdn[1] before but they seem to have changed their pricing recently, but they do allow you to pay upfront and they do email out cheaper deals about every month for large-ish amounts (5TB and up).
[1]: http://www.maxcdn.com/