its good when you get a topic everyone can get involved with on the entire forum!
music is a good suggestion. big events in the world (such as rita topic) everyone has an opinion on music, and world events.
Contraversial things can be fun to talk about, such as debates on certain topics
i suppose it all depends on the person really!
EDIT: the polls are a good wee feature, shame they aint used much
some tv program threads are good, but not everyone watches popular tv programs.