I second the Idlewild "Rosability" nomination (and add "I Am What I Am Not" for its anthemic qualities.

And the La's, as per usual, are direly underrepresented at #45 with "There She Goes."

Though I'm not really so sure that song is a anthem, really. According to dictionary.com, an anthem is:

1. a song, as of praise, devotion, or patriotism: the national anthem of Spain; our college anthem.
2. a piece of sacred vocal music, usually with words taken from the Scriptures.
3. a hymn sung alternately by different sections of a choir or congregation.

To me, "I Predict a Riot" is anthemic. "Don't Look Back in Anger" definitely is not.