Investing/Strategies / Bonds & Fixed Income Investments

I have a decent amount of money sitting in a money market account, barely making anything. I'm already putting a decent amount of my salary in a retirement savings plan, so I'd like to do something else with these savings.
I know that muni bonds are fed-tax free.  What kind of payoff could I expect from this?  If I put, say, $50,000 in one, what kind of monthly payout could I expect?  Are muni bonds the best option, or are there other investments I should be looking into?
Thanks.