Saku Koivu for the Montreal Canadiens. Was a class act, without question, throughout his entire career, never complained when he was playing with horrible players on awful teams, matured into a leader, battled injuries, battled serious health issues and always came out on top. Natural leader, classic set by example kind of guy and really understood what it meant to be a Montreal Canadien and to represent the franchise. Virtually all of his peers in the long history of the Canadiens - and they have a lot of guys that fit the bill of this question - are Hall of Famers and Stanley Cup Champions. He spent a large chunk his career with poor rosters, but he never sulked, he never asked for trades and he never complained. Even when the ravenous Montreal media behaved in deplorable ways (once, while hospitalized after getting a Justin Williams stick in the eye, a Montreal press member snuck a flash photo through the window of Koivu's hospital room, at a time when the flash could have caused serious damage to his injured retina. Still Koivu didn't lash out.)
It was a shame he was allowed to leave. He should have spent his entire career with the club.