We spend a lot of time talking about how digital media will increasingly be free, and how this will unleash a wide spectrum of disruptive opportunities for entrepreneurs and investors.

To that end, let's talk about what type of media you can sell, and what you can't.

What you can't sell

Well, can't is a strong word, but what will be increasingly difficult to sell -- what is essentially a dying element of the value chain -- is mass-market products. Think things like books, compact discs, DVDs. This is a huge chunk of the publishing industry -- which is why I think it is such a great entrepreneurial opportunity, as the diminishing revenues of sector incumbents signals the industry is ripe for disruption.

What you can sell

Time-sensitive information. For instance, a stock trader who publishes buy and sell signals can charge for his content.

Customized products. Josh Freese, an f'ing fantastic drummer, offers to write you a song for $20,000 USD. And here I been doing it for free!

Private communities. I think private education communities, where you can be assured of an intimate environment and attention from community "stars," will become increasingly feasible. This is very similar to customized products, as they both follow the trend of monetizing small things and activities -- i.e. small is the new big.

Here's "Bright Future in Sales" by Fountains of Wayne.