For New York City families, there is a terrific list of both summer and school year programs on the website of InsideSchools.org. The list is organized by interest area: math, science, arts, humanities, and academic prep. All of the programs are free.
The folks at New York City's Resources for Children with Special Needs have extensive listings of camps for children with issues ranging from ADHD to medical disabilities. They have a new "camp match" program that allows parents to find camps specific to their child's needs.
A national program, with locations from New York to Hawaii, After-School All-Stars partners with schools and both local and national organizations (such as the NBA) to provide after-school activities for school age children who need a safe, fun place to be after school and who can benefit from academic support offered in such a setting.
The American Camp Association website offers information on the more than 2,400 camps they accredit and provides information and tips on camping for parents and children on everything from how to choose a camp to how to deal with homesickness