Quit your job! - (37signals)
A very nice point made in the article above about the whole "startup" thingy. Its not just the billion dollar dreams, VC funding, eyeballs, termsheets, IPOs that make entrepreneurs and define what they do. Its the following-your-heart on a lark, not necessarily being bogged down with growth and targets but the desire to achieve something that is either creative, or redefines either you or what you do. I'm not saying the growth and dollars should not be part of this, just that they're non-essential ingredients for some forms of entrepreneurship.
BrewHaHa, The Rainwater Club, BumsOnTheSaddle are a few that come to mind, and heart :)