NASHVILLE, Tenn. - More than a few people in town wondered what was up when Robert Plant was spotted in recent months at the Grand Ole Opry and at the popular bluegrass club The Station Inn. The former Led Zeppelin frontman's album with bluegrass star Alison Krauss, "Raising Sand," will be released Oct. 23 on Rounder Records, the label has announced. Recorded in Nashville and Los Angeles and produced by T Bone Burnett, the album finds the two interpreting lesser-known material from blues, R&B, country and folk songwriters including Mel Tillis, Townes Van Zandt, Tom Waits, Gene Clark, Doc Watson,...