Babe I'm going to leave you is a good one, "Wish you were Here" by Pink Floyd is a good, but I don't know if you would consider it acoustic. "Life by the Drop" by Stevie Ray Vaughan. I can' think of anymore right now. And "Dee" by Randy Rhoads is about the only classical song by rock band that I know of. "Tears in Heaven" is a good acoustic song regardless if Clapton is blues or rock or what he is.