What is the best alternative revenue source to advertising for a media business model?

One way to look at it is to assume that consumers don't (like to) pay for content, they pay for access to content.  Advertising allows 'free' access to content, but with at time/distraction cost of the ad.  For some that's a low bar.  If you want to offer an alternative, you have to provide value in the access portion of the equation, either exclusive material as Nathaniel Schick mentions, advanced search, tailored curation or ease of device integration (eg itunes/ipod). I wrote a blog post a while back on this topic:  http://wp.me/p1Ch1q-p

If you are serving media and looking for alternative revenue streams over selling ad space, there are few options. You either go with a subscription or pay per use service offering. Many industry specific magazines have used this tactic for years to be highly profitable while minimizing the ads they had to sell(assuming a solid user base that is). The only downside of a subscription service for media, is that you need to have something that is not readily available for free somewhere on the internet. There is another option to monetize your media business model and that is the collection, use and sale of personal data. It's the reason that Facebook has such high value in marketers eyes - the personal data and profiles that can be structured from it are incredibly useful to any business. This has it's own challenges beyond the fact that you need informed consent to really sell someones date, in that you need a pretty robust data capture system along with some other tools to actually turn the data into something valuable. Hope that give you some options.