Just a random thought that I was curious to see what people would do. Also the numbers were off the top of my head and I have no idea how viable they are for the situation. The risk was added to mitigate obvious hi-risk hi-return options (e.g.- gambling)
Super high-risk: go to freelancer.com / elance and pay a freelancer to build the next top-grossing app.
Low risk, low return: Open a savings account, although with interest rates lower than inflation, you'll probably lose money in real terms.
Also, 0% risk.
Obligatory disclaimer: I have bitcoins and I think they are awesome. Also, if BFL ships and you can get one of their miners, it will likely give an easy 15% ROI (and probably be relatively liquid)
Even so, a 20% gain probably isn't that big of a deal. A random growth fund can do that.