A Book of Five Rings - Go Rin No Sho: Complete text of a translation by Victor Harris of Musashi's most famous work.
A Book Of Five Rings By Miyamoto Musashi: Complete text in English.
Miyamoto Musashi's Book of 5 Rings: Analysis of the book with extensive English test, plus the entire text in Japanese.
Samurai Archives: Miyamoto Musashi: Biography and an illustration.
Wikipedia: Miyamoto Musashi: Extensive article with references and works.