I think Sports woud be a major forum topic. There's always something going on in major sports that captures the interest fo the masses. There's always some controversy. There's rivalry and heated debates. The nice thing about sports is that everyone is an expert, even if all they have to go on is a computer and a TV.
And there are personal sports interests and experiences that could be discussed in a Sports Forum.
[bragging]Hey, just yesterday, my son went to a minor league baseball tryout at the invitation of the Pittsburgh Pirates ... that was a fun experience, even though he didn't make the cut this year. He's still got time.[/bragging]
There are other sports forums, some using vBulletin, too, but none with the community of the Cellar.