John Fogerty's first great albums were with CCR starting in 1968, and his latest was Revival in 2007. It's a really good album (and it's available on emusic). Van Morrison is another long term prolific writer with releases stretching from 1967 to 2009. He hasn't had a big hit in a while, but the critics consistently give him good reviews. Tom Waits hasn't had a release since 2004, but he has 30 years of consistently good material. And of course you have to give a nod to Pete Seger. He plays traditional folk songs now more than original compositions, but he's been performing and recording steadily since the late '30's. But those are all individuals. It's much harder to keep a band going over the long term. R.E.M has 25 years worth of great music (so far). And although I'm no longer a fan, I have to give credit to both AC/DC and Aerosmith, who have been making records since 1975 and 1973 respectively, and who have shown much more staying power than most of their peers by managing to avoid turning into a nostalgia act.