Listening to Jerry Remy and Dennis Eckersley in the NESN booth for Red Sox games has been an absolute joy these past few years. Maybe it's because I love the era of baseball in which they played, but they are must-see TV for me.
Andy Brickley also does a great job with the Bruins. And to go way back, John Pierson, doing color with Fred Cusick, was excellent on Ch. 38.
nationally, I liked listening to Tony Kubek when he was paired with Garagiola or Costas. I thought he would explain all the nuances to the game that a casual watcher wouldn't understand.