If you took all of the economists in the world and stacked them end to end -- it'd be a good idea.

If you took 10 economists and lined them up, they'd all point in different directions.

Q: How many economists does it take to screw in a lightbulb?
A: None, the invisible hand will do it.

Did you hear the one about the economist who drown crossing a river that was an average of 2 feet deep?

I always liked this one:

"If you took all the economists in the world and laid them end to end, they wouldn't reach a conclusion."

That's the one I remember.