I was updating some lecture notes on option volatility and was doing a little research on the various VIX (S&P 500 implied volatility) products that are out there these days. It turns out that there are a whole host of securities (mostly ETNs) that allow an investor to trade various futures positions in the VIX.
Consider the following post on the blog VIX and More. At the time of writing, you can trade leveraged 5 month VIX futures or if you're wanting to go short volatility you can trade an ETN that takes a short position in 1 month VIX futures. The graphic at the bottom of the post shows the different products.
A lot of these have fairly small trading volume, so you have to wonder about liquidity. They also look pretty risky.
Personally though, I'll just stick with my index funds.