If you do have cash in a money market, you should know which kind you have.  The New York Times does a good job of explaining the difference:

A money market deposit account, on the other hand, is entirely different. It is an interest-bearing bank account that is insured -- up to $100,000 per account and up to $250,000 for some retirement accounts -- by the Federal Deposit Insurance Corporation. Joint accounts are insured for $100,000 per account holder.