I guess it is a matter of terminology but I have to disagree on this one. A bubble is all-pervasive and extreme. It represents a systematic investment mania where everything becomes surreal. People sell vast tracts of land for a prized tulip. Junk companies with nothing to offer but a vague concept about revolutionizing how this or that will be done owing to some new phenomenon such as the internet make serial stock…
This is a great point. To condense what you said a bit: the dot-com bubble followed the democratization of stock trading (which itself got a technological assist from the internet). Lots of people, myself included, who never bought a stock start using online trading accounts. The housing bubble followed the democratization of home buying. Lots of people who never had bought a house before (or a second or third house)…
My boring answer has always been: commodities. Yeah, ordinary people can buy and sell precious metals now. But wouldn't it be more convenient if you could just directly buy a nicely packaged product online (with no service premium) that represents whatever arbitrary commodity or commodity future (or whatever it is you trade) you desire? I'm sure this would do wonders for oil prices. All those gold trading services that advertise on cable seem to be a niche example of the phenomenon.
However, I just came across something which may offer a more interesting answer: bitcoin, or more generally, currency. I going by what I was just reading here:
http://www.reddit.com/r/programming/comments/g7zlw/google_en...
I don't fully understand what bitcoin is. But I'm sure that will only be part of its charm if it ever goes mainstream. At any rate, just an idea.