For whatever reason, some players get recognition and some don't. It's amazing how some very good players often stay under the radar or are significantly underappreciated by fans and the media. I guess personality plays a role in it. The market in which a player plays clearly affects the perception as well.
Let's take a look at my All-Underrated Team, position-by-position:
First base: Darin Erstad, Los Angeles Angels
He's a three-time Gold Glove winner. This guy is the first player ever to be awarded a Gold Glove as an infielder and outfielder and the first to be recognized at three different primary positions (left field, center field and first base). He offers a tremendous amount of flexibility to both the manager and general manager. Erstad is also one of the toughest players in the big leagues.