Annuities are one such tool, and can hedge against periodic losses in the market that happen as sentiment ebbs and flows. They also grow tax-deferred, so what you put in grows a little bit bigger through the power of compounding before you have to give your part to the IRS when you make your withdrawals.
Just like it's important to diversify your stock portfolio, it's also important to diversify your types of investment tools. This helps prevent any kind of upset that might come from having all your eggs in just one financial basket.