Left-wing group co-founded by Morris Dees. In the past has sued the Klan and taken other legitimate actions towards civil rights. However, since the near-demise of the KKK, they've lately spent some time spreading scare stories about a rise in "hate", naming "hate groups", and strongly supporting illegal immigration; those keep the donations rolling in.
Past or current member of the Border Human Rights Working Group headed by the Mexican government-linked Peter Schey. Frequently cited by the mainstream media as a credible source. Their Mark Potok misled about hate crime statistics, with his claims since repeated countless times by the MSM.
See also "The church of Morris Dees" from Harpers Magazine (link, link), the quotes from Jim Tharpe of the Montgomery Advertiser here, a "watch" site here, "Southern Poverty Law Center Pushes Twisted Definition of 'Hate'" (link), this, Mark Potok, and Heidi Beirich.