From Wiki:
Fox: Saturday afternoon Game of the Week on a regional basis; eight appearances per team. In addition, the network will broadcast the All Star Game, the ALCS and World Series. The network is canceling their pre-game show, and will now start games on Saturdays at 4 PM US ET/1 PM US PT, except for three dates (April 18, and May 2 and 9) due to NASCAR coverage, when those games start at 3:30 PM ET/12:30 PM PT.
ESPN/ESPN2: Sunday Night Baseball on a weekly basis; five appearances per team. In addition, there are games on Monday and Wednesday nights, with the Monday games moving to Friday nights when the 2009 NFL season begins, Opening Day games on April 6, and the Home Run Derby on July 13. ESPN Radio will also carry the Sunday Night games, as well as selected games through the season and the entire post-season.
TBS: Sunday afternoon games starting on April 12; 13 appearances per team. In addition, the network will carry the announcement of the All-Star Teams in the National and American Leagues on June 29 as well as the Divisional Series and the NLCS as per the alternating contract with Fox.
MLB Network: The network plans to carry a weekly Thursday Night Game of the Week starting April 9. No word on the limit of appearances any team can make as of yet.