A great way to gain access to hundreds of museums nationwide is thru the ASTC (Association of Science-Technology Centers) passport program. Purchase a pass at one of the participating centers for free or reduced admission to other centers throughout the country. This is an excellent resource for traveling families.
We purchase our passes through a center in Florida, which is very reasonably priced for a family. We more than get our money's worth. One trip to a larger science museum and your pass just payed for itself.
Find a complete list of participating centers at: