Influential Producers

I've always found it interesting how much a producer can influence the sound of an artist. The right synergy between the two can make a good artist great and really shape the creative process. A few influential producers come to mind: John Levanthal (Rosanne Cash, Shawn Colvin, Marc Cohn), Ethan Johns (Ryan Adams), Tommy Lipuma (Diana Krall). Sometimes I shop recordings by looking for producers who have worked with some of my favorite artists--it doesn't always guarantee a great recording but it helps narrow things down as the producers mark is usually evident no matter which artist is involved. Anyone else look at the credits and see patterns?