The economic boom in the 90's was largely driven by the hi-tech bubble. After the bubble burst in 2000, America found a new frontier, the real estate and financial derivatives. Most of the economic development in the past few years seem to be related to the real estate bubble and the stock or financial tricks.
What is going to be the next bubble?
One likely candidate is the alternative (or renewable) energy, green technology, initiative.
If there is a real substitute for the gasoline (and petroleum to a larger extent), and if this substitute is low cost, low/no pollution, and unrelated to coal or petroleum, the potential market for this technology would be huge. However, if it turns out to be a disappointment, the downside could also be a lot of wasted resources, research, funding, etc.