I've previously raved about the feature stories on ESPN 30 for 30. If you love sports documentaries but can't always devote 1 1/2 to 2 hours, then there's E:60. If you only have 30 minutes, then I strongly recommend SC Featured.
Archives of SC Featured stories can be found at the WatchESPN archives as well as ESPN's YouTube page.
Here's the story I finished watching a few minutes ago.