Musashi is also one of my favorite historical warriors as well. I've read several translations of his book, Go Rin no Sho, and tried to get my hands on whatever books about his life and accomplishments were available. I have a few of them in pdf form, so I will upload them later.
Other than Musashi, there were a few other Japanese swordsmen that were undefeated throughout their lives, like Tsukahara Bokuden or Itto Ittosai. They also developed different swordsmanship styles. What I liked about Musashi most, other than his martial skills, was the attitude of self-reliance he had and that he didn't conform to the norms of society at that time (it was customary for known swordsmen to open schools under the patronage of a lord or serve as instructors to the shogun). Instead, Musashi just kept traveling from place to place without remaining the retinue of a daimyo (at least until he went to the Hosokawa).
By the day, that drawing of Musashi comes from the Vagabond manga, which is about Musashi's life, and I highly recommend it, it's an excellent series. A mix of historic facts and fiction, but you definitely should give it a try, even if not for Musashi, it has sword fights and it's really well drawn.
There is a fiction novel written about Musashi, by Yoshikawa Eiji, which I also recommend.