[dandersh]

The Dixie Chicks.

Country stations stopped playing their songs because listeners would call in to complain, threaten boycotts, etc.

While I'm struggling to remember exact successes, I know the Parents Television Council would use petitions to cancel programming that they deemed inappropriate.

[jimbokun]

I think the Parents Television Council was largely unsuccessful.

They hated the Simpsons, which is now the longest running show in US history, I believe.