SocialAction.com has a great collection of Passover readings on social justice issues. Check it out here.
Reb Arthur, at the Shalom Center, has a large collection of writings on Passover: You can view them all here.
Also, on Jewschool, Radical Torah’s contributing editor Sarah “Shamir” Chandler has compiled a list of online Passover resources, including some social action related materials. You can view the complete list here.