This may depend on your philosophy about money. I tend towards despising debt, so consider my perspective in that light. Others will disagree.
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Pay it off. I'm not sure what your mortgage rate is, but let's say it's 6%. If you were put your money in the market would you be guaranteed a return of 6%? Hardly. If you were to stick it in bonds, you may be able to eek out close to that rate, but your money's locked with the potential for price fluctuation until maturity. What if you need to access it? With a home, you can draw from it if you set up a line of credit in the mean time. In addition, your housing expense drops significantly. With the extra money you can fund a sizable emergency account.

One other consideration - if you pay off your mortgage, that monkey's off your back. I've had one home paid off in the past. It was great! I didn't really utilize the situation the way I should have, but it was a wonderful feeling. I'd love to be in your situation again - congrats, suzyq!

You can pay off your mortgage and then open a heloc so you can use your equity for a hot deal or ?? There are some areas you can buy foreclosed homes for 20-30 cents on the dollar and flip them quickly or rent them out for positive cash flow.

I agree with Impact. Pay off the mortgage and open a HELOC. You can draw on that if and when needed, for whatever you need. They are usually low cost to open, and you would only pay interest if and when you draw funds out.