National Conference of State Legislatures: Felon Voting Rights.
American Civil Liberties Union: Felony Disenfranchisement Laws.
National State Center for Courts: The Future of Restoring Voting Rights for Ex-Felons.
The Sentencing Project: Felony Disenfranchisement.
Note: each of these are interest groups. They're covered in the chapter on Interest Groups and Political Parties. The ACLU is also prominent in the chapters on civil liberties and civil rights.
From pro-con.org.
