There are also bitcoin related stocks to invest in.
www.havelockinvestments.com is one of the more popular exchanges at the moment.
But these companies and exchanges are very risky. 

Some gambling sites allow you to play the role of the banker.
www.just-dice.com is one.

But check into these before investing.  Try to find one with a good trust rating - like ASICMiner (AM1 on Havelock).

Interesting article. 
Thanks.