Forums (or Fora, for you Latin geeks)
I recently subscribed to a satellite tv package when I upgraded my DSL account — and I instantly got hooked on that adorable Animal Planet show “Meerkat Manor.” Just in time for the season ending. 
Then I started watching Orangutan Island, and while watching the 2nd episode I idly checked the whois for orangutanisland.com. That domain was taken, but orangutanisland.org was available, and I thought to myself, I wonder if I should register that and set up a forum for people to talk about these cute critters? So I did. I used the free phpBB forum software for the forum, and also created a small collection of static informational pages so that the site would have some content to rank for.