Social Studies

World Factbook-A wealth of facts and figures about every country in the world. Compiled by the United States Central Intelligence Agency.
http://www.cia.gov/cia/publications/factbook/index.html

National Geographic-Use "Find a Place" for maps and a digest of information on every country. Searchable and zoomable maps, including physical/satellite, climate, political and cultural. Country flags, facts, and demographic information.
http://www.nationalgeographic.com/resources/ngo/maps/

Hyperhistory Online-Timelines of every historical period, with indexes/biographies for people and events.
http://www.hyperhistory.com/online_n2/History_n2/a.html

Science

Bill Nye the Science Guy-Fun with science.
http://billnye.com/billnye.html

Cool Science for Curious Kids- A fun and interactive site to help kids appreciate science. Includes activities adapted from various science museums.
http://www.hhmi.org/coolscience

Math

Math Glossary- A boring name but a great site with illustrated and animated definitions and explanations of math terms. Searchable by grade level.
http://www.hbschool.com/glossary/math

Super Kids Math Worksheet Creator-Just in time for summer! Create your own printable math sheets.
http://www.superkids.com/aweb/tools/math/

Art & Reading

A. Pintura-Art Detective-Improve your reading and problem solving skills while also learning about artists like Picasso, van Gogh, and Gauguin as you help solve this art mystery.
http://www.eduweb.com/pintura/