I got interested and started studying the markets over 2 years ago and with the crisis in our financial system I have done a lot more research in to the commodities markets. In comparison to paper assets these markets are very small and demand is increasing world wide. I have also seen articles online about increased interest in fine art work and wines. If you wanna go with something like diamonds be sure to do research and look in to rare colored diamonds as there is supposedly only 1 colored diamond in every 1000 diamonds.
I think the best and most affordable bets on precious metals are in Silver and Palladium because these have a lot less hype surrounding them, have many uses other than jewelry, and are considered money by the ISO. (See
http://en.wikipedia.org/wiki/ISO_4217)
If you feel its necessary to be in the stock market you should look at trusts, and commodity and short/inverse ETFs.