If you're asking for underrated players, that's one thing, but if you're asking for players who had a huge impact for many years, and contributed to the team's success more than people realize, then...
Bryant Young -- He got plenty of accolades, no doubt. Madden once said (around 1998), if he could take one player from the 49ers to play on his team he would take Bryant Young.
He was a quiet leader of the defense for many years and had to face double teams the rest of his career when Stubblefield left, because he was the only true force we had on the line after Stubblefield left.
Without him, our D-line would have been very sub-par. He was like a bigger, more athletic Justin Smith.
Every coach and player on the 49ers had total respect for BY. He was an unselfish player, who stayed on his assignments to help his team rather than help his stats (although his stats were impressive).
Gary Plummer -- One of the most unsung stalwarts of the 49ers defense. Ken Norton might have received more recognition, but Plummer was the better linebacker.
Always plugging running lanes with perfect technique and execution, always taking superior angles. Coached the players around him, diagnosed plays pre-snap at a high level of accuracy, adjusted the D-line.
Had limited athleticism, but played with his heart and soul. Again, like BY, well respected and liked by players and coaches. A man's man. If BY was the heart, he was everything that made the structure solid.
Tim McDonald -- If BY was the heart, and Plummer was the structure, Tim McDonald was the soul.
The vocal leader of the defense, who talked the talk and walked the walk, like a Rodney Harrison type.
Tim McDonald always seemed to be in on the play. He always seemed to make the critical interception, he always seemed to make the important tackle.
If BY's pressure wasn't enough, it was OK because McDonald was back there in the secondary.
If Plummer couldn't catch the running back, it was OK because McDonald was up at the line of scrimmage making the tackle.
One of the best free agent signing's in 49er history. Was perhaps overshadowed by the Woodson's of the era, Darren and Rod. McDonald was only a notch below them as an athlete, but was every bit their equal as a football player and leader.
When you combine leadership, talent, and heart. These three players are the most underrated in 49er history that I can remember.
49er offensive players like Montana, Rice, Craig, etc I feel are already well known and recognized.
[ Edited by BrianGO on Mar 21, 2010 at 19:37:22 ]