What we need is a high profile, trusted figure to raise the issue of liberal bias and spearhead a campaign to put those organizations out of business. Canceling subscriptions, publically calling to task the offenders, calling for resignations, and mass actions like petitions and email campaigns would be the tools.
If George Allen did this, combined with his stance on the illegal immigration issue, he'd be a shoo-in for President in 2008.
Contacting and boycotting advertisers would be effective as well.