I am currently reading Sandra B. Tooze's biography of Levon Helm. Fan-freaking-tastic! She had previously written Muddy Waters: The Mojo Man, which I guess will be next.
Robbie Robertson's Testimony is excellent, much better than I had anticipated. It's the most complete accounting of The Band I've read. Another very good book on them is The Story Of The Band by Harvey Kubernik.
Outlaw Blues by Paul Williams is a compilation of the essays the author wrote for Crawdaddy magazine in the late-60's. Two chapters provide the best behind-the-scene reporting on the recording of Smile, the aborted concept album undertaken by Brian Wilson and Van Dyke Parks in 1966-7, published as the recordings were taking place. Essential reading imo.