I still like the original Doom Shareware model. They gave you what felt like 1 whole game for free, enough that really impressed you and gave sense of a complete product.

Then they made an offer of 2 more games (or episodes) for a fee. When taken as a whole, they were only giving 1/3 of the game away for free, but before purchasing, you felt like you were given an entire unit upfront.

This established a great relationship between the user and ID software. They demonstrated for free what 1 unit of Doom was, then offered 2 more -- which I roughly understood what value I would get.

I think creating and segmenting units of a product that are complete in themselves, but related to other premium offerings is a great way to get a user to feel both satisfied with a free product but yearning for more. It also shows that segmenting your sales narrative in freemium is very important. I get irritated when you interrupt my free unit and offer the rest at cost. I am happy when I receive a whole unit for free, then am offered more units for a fee.