Silver
Throughout the first 10 years of the 21st Century silver has been quite cheap. What has happened lately is that while gold has been zooming up into the stratosphere, to well over $1000 per oz, silver has barely moved from $20 or so. What this means is that silver is very likely to move up in price in the near future.
Another indicator that silver is about to go mental is the fact that silver is not only a monetary item but also an element in high demand in consumer electronics and elsewhere. Indeed, at some point it may become the reality that there is more tangible gold on planet Earth than silver. As I said, silver could go mental - depending upon how rapidly people lose faith in current fiat currencies.