The best steel-string acoustic specialists Ive heard are Michael Hedges(RIP),Tommy Emmanuel, Leo Kottke, Tony McManus and Adrian Legg. They've pretty much taken finger picking to the max. For sheer technique, you cant beat flamenco players like Pace de Lucia, Paco Pena and Tomatito. For acoustic flatpicking the master is Clarence White..of Byrds fame (also RIP). Among rock players, Eric Johnson's about the best I've heard.