Probably the best bargain out there amongst sports audio.
You get a year's worth of live Major League Baseball games. Every game is available with your choice of the home or away radio station's announcers (plus alternate audio for teams like the Diamondbacks who also broadcast in Spanish). If that wasn't enough, you can also listen to past games in the archive.
A whole year is just $15. MLB.com has other subscription choices as well, but if you like listening to baseball, this is a no-brainer.
Update: in case anyone cares, it looks like the internet broadcast is approximately 45 seconds behind the radio broadcast. Also, as best I can tell, not only can you access 2007 game archives, but 2006 as well.
Note to the NBA: you need to start doing this! I'd love to listen to Al McCoy broadcast the Phoenix Suns games. I'm sure I'm not the only one who is a fan of the broadcasters as well as the teams.