A money market account is safe and leaves your liquid assets in a state where you can get them easily. The downside is a poor rate of return.
Tax-exempt bonds (local, state or federal) are an attractive option provided that the rate of inflation doesn't exceed your rate of return or reduce it to effectively nil.
Another sensible option would be to pay off any debts you have. Your income is your best way to grow wealth, and every dollar you pay in interest is a dollar taken away from your future earnings. Even though this isn't as exciting an option as putting your money in the stock market, this might be your best bet longer-term.
If you have no debt, then the $50k would go a long way towards a down payment on a home - that way you can stop paying rent, which is another source of wasted earnings.