Michael Mace gives a great summary of media and mediums in a blog post and goes on to say:
The transcendent need for a billing mechanism.
When I said that the Web is a tool for creating new media, I left out an important detail. It’s three-quarters of the tool. We have a great delivery system, and Google is well on its way to dominating the advertising part of the financial model. What’s missing is a standard mechanism for people to pay for content that’s not supported by advertising. Some types of content work fine with ads, but I think some other types are better when paid for. Novels, short stories, music, and research reports all qualify. Creators and readers would both benefit from a system in which people could easily pay a few dimes or a few dollars directly to the author, but today we generally have to fumble with credit cards and awkward systems like PayPal. And credit card vendors strongly discourage small payments.
A few posts later, he covers a service from Amazon which will help sites all sizes charge for their services.
This could mean you!