I can't think of too many songwriters who are self-important enough to publish poetry. Can you? I s'pose you got Leonard Cohen going in the other direction (poet writing songs), and few would argue that Dylan is a bona fide poet. Also, I have John Lennon's "In His Own Write", which came out in '65 I think. Light, clever stuff. I've seen Paul Kelly (very good Australian singer/songwriter) publish his lyrics as a book of poetry, but that's not quite the same thing. I also have David Duchovny's very strong book of poetry ("Why Me?"), but I've never heard him sing.