If you're really serious about your baseball and like the idea of managing a team from minor leagues through to the majors, "Out of the Park Baseball 2007" for the PC will probably be right up your alley.
Simon over at TTGamer checks it out in detail.
Sports Interactive are a developer you would know for the famous Football Manager series. They have taken the football management genre and made it their own, producing year in year out the best football management game out there. However, they do a few games in the 'off season' which are of equal quality and one of these has just been released in the form of Out of the Park baseball, right in time for the MLB season in the US. While OOTP baseball is not as licensed or refined as FM, there are definite similarities between the two and Sports Interactive have built a very useful game for those looking for a baseball management sim.