There are a fair number, but the standard text is still To Purge This Land With Blood by Stephen Oates. It's a pretty conventional cradle-to-grave biography that tries to talk about everything and is probably a little too critical of him, but the newer alternative John Brown, Abolitionist: The Man Who Killed Slavery, Sparked the Civil War, and Seeded Civil Rights is a bit too far the other way...and I say that as a guy very fond of Brown.