Other
Menorah Ministries: The Star of David
A detailed description and history of the famous Hebrew symbol. The article states that the symbol can not be traced to King David himself but that the use of hexagrams was found in Jewish magic dating back to the 6th century C.E.
Wikimedia
Wikipedia: Star of David
A detailed entry on the history, symbolism and current usage of the Star of David. Also has nice illustrations.
Israel Ministry of Foreign Affairs
Israel Ministry of Foreign Affairs: King Solomon's Seal
An article which explains in detail the famous symbol of Judaism also known as the "Star of David".
Other
Jewish Encyclopedia: Magen David
A short but informative article on the famous Jewish symbol also known as the "Star of David".
Judaism 101
Judaism 101: Magen David
A nice description and history of the famous Jewish symbol. The information is from an Orthodox view.