I think next bubble has to be something hi-tech, something that only Americans can do (at least at the beginning), otherwise there is not point.
Nanothechnology? Real alternative energy? Flying cars? Android robots?

All we need is, take a couple of recent scientific papers, popularize them and create a hype in the media. Money will start to flow in the sector, millions will start working on it… Anything remotely related will skyrocket in price.
After several years there will be some results, not as good as everyone expected, but still pretty nice. At that point the bubble will burst. What happens after that is not our problem: there will be enough blogs discussing it then.