Anion-pi interactions are attractive interactions between electron-poor aromatic rings and electron-rich negative ions or groups. Predicted by theoretical studies in the late 1990s, the first experimental evidence of anion-pi interactions was provided by two independent studies in 2004. Since then, the role of these interactions in chemical and in biochemical systems has been investigated. In this work we report benchmark interaction energies, estimated from the extrapolated MP2 basis set limit with CCSD(T) correction, for several model complexes. These are then used to assess faster, more approximate methods including MP2 and its local approximation, along with various forms of Density Functional Theory (DFT). The most promising of these are then used to describe the geometries and interaction energies of a series of complexes between electron-poor substituted benzene rings and anions as well as examples of such interactions in models of proteins.