Your best bet is to speak with a financial advisor.
No one here can really answer that question for you, since we do not know what your time horizon is or your risk tolerance.
For example, if you needed to double your money by tomorrow and you have an extremely high tolerance for risk, then someone could advise you to gamble the $3000 at the casino.
However, if you have a very long time horizon (i.e., many years) and a very low tolerance for risk, someone could advise you to invest in U.S. Treasury Bills.
For anything in between, there's the stock market, options, futures, real estate, gold, silver, fine art, antiques, etc. etc.
Call a financial advisor.