Museum Day 2009 is on September 26th, 2009. You can get admission for 2 to any participating museum. Here is a link to the free admission cards from Smithsonian Magazine. Great deal! :)
Search for the museums by state. One of the participating NY Museums is the Adirondack Museum, great time to visit the Adirondacks and see some awesome fall color besides! Go here beginning September 9th, 2009 for the latest fall foliage updates.