I had tried doing a game startup together with another guy, but so far we rather failed selling our first (and only) game. But afterwards I learned about another business models rather accidentally - advertisment for myself. We kept our website up and just having finished a good looking game was enough to get people interested in working with me. I do now freelance work and that game is my main selling point.

Also missing in the list was that you can certainly also sometimes sell the technology of your game.