One source of information about your family that many researchers don't know about or overlook are the unclaimed property records. When a bank or business has unclaimed funds such as account balances, paychecks, safe deposit box contents, and insurance refunds and proceeds, they are required to send the money/property to the state after a required holding period. All of the states have searchable online databases so people can check to see if any of the money/property belongs to them. I search these databases occasionally looking for old accounts family members may have left behind. Thanks to our research, it's usually easy to prove ownership of the property, or at least that you're related to the owner.
For more information, see http://unclaimed.org/mainframe.asp?VisitorType=owner
Unclaimed property records are not maintained by the same agency for every state. You can also go to the state home page and just search for "unclaimed property" to get to the correct agency. Don't wait too long. A lot of states are only required to hold property for a few years. After that time passes, the cash belongs to the state and the property can be sold (I think Texas sells property, e.g. jewelry, on ebay).