If you have Google as your homepage, this is the best standings tracker available... because you can make it show only the races you want to see, and weight it for the teams you're actually watching.
Yeah, Google is watching you, but I like this plug-in that much. Just click "edit settings" from the top-right arrow, then check boxes you want to see, and rank the teams so your favorites float to the top. Includes Wild Card races, live links to Gameday, probable pitchers, and starting in September... the option to view the Magic Number.