Some libraries have museum passes. If you go to your local library you
can request a museum pass. The passes get you into museums for free or
for a discounted price.
There are also museum groups
that you can join, that have museum locations all over the U.S. They're
usually reciprocal, so once you join you can get into <a href="http://www.campingroadtrip.com/outdoor-living-newsletter-november-2010/discount-passes-to-childrens-museums/" target="_blank">"satellite"
museums for free</a>.