For a GREAT many visitors, the answer would be "Other: Image of the Day." I don't know what the numbers are, but I understand that a lot of people come just for that. Of course they're mostly lurkers, and they mostly don't wander from the IotD section... so they'd never even see this thread.
For myself, it's a combination of things... for one, you can't swing a dead cat around here without hitting somebody smart. That's important. For another, you can't swing a dead cat around here without hitting on of Jimbo's threads. That's also very important, because... I don't know how to finish this sentence.
There are two things which satisfy my intellectual lust... intelligence, and humor. But since I can't find either, I come here. Har har!