There are many landmarks related to the battle in Arimatsu. To tell you the truth, I wish there was a museum to display the artifacts. It is a shame that the Toyoake battlefield's museum was closed down. That is not right at all in my opinion.
I wrote about Matsui Munenobu's location during the battle in December of last year. He was a retainer of the Imagawa and was also the lord of Futamata Castle in Totomi Provice. During the Battle of Okehazama, Matsui Munenobu was killed in action. His two graves can be found at Chofukuji in Arimatsu and the Toyoake Okehazama battlefield near Kotokuin.
Here is the English explanation of the battle and a street sign leading the way with a the 2010 450th anniversary banner.
Here is some more information Hachisuka Koroku's role during the battle. Ota Mitsuaki's Okehazama no Shinjutsu, pp. 126-127. Ota noted down the goods that were provided to the Imagawa troops. The goods included mochi, sake, and kombu. He mentioned that Hachisuka did play a role in stopping the Imagawa rapid advance.
Nobunaga no tame!