Source, The Onion.
The Onion has some other suggestions:
Current bubbles being considered include the handheld electronics bubble, the undersea-mining-rights bubble, and the decorative office-plant bubble. Additional options include speculative trading in fairy dust—which lobbyists point out has the advantage of being an entirely imaginary commodity to begin with—and a bubble based around a hypothetical, to-be-determined product called "widgets."
I'm banking on "The Future" being packaged up into futures, myself.