Off the top of my head, Bonnie Raitt, Raun MacKinnon, Paul Simon, John Renbourn, Dan Hicks. And of course Richie Havens, to the tune of a couple D-40s a year. Hicks, Bonnie, and Dave Van Ronk are (or in Dave's case, used to be) long-time F-50 loyalists, and . Renbourn fiddled with his D-55 for a long time, trying to get the sound he wanted (he sanded the finish off at one point) before switching (to a Franklin, if I recall correctly). In almost every photo I've ever seen of Tom Smothers, he's holding a D-55 (unless it's a D-100--in any case a fancy Guild dread). (I have seen him with a Martin D, but only once that I can recall.)