Atlas, Polar, FedEx, Cargolux, ABX, DHL Air, LH Cargo, MNG, TNT, UPS etc are IOSA.
But IOSA certificate has nothing to do with the real safety & quality level, and absense of IOSA more often reflects unwillingness to spend money for another piece of IATA paper. Too many airlines realized that, IATA started to invent more rules around it, setting IOSA as a requirement for codeshares and interlines, so those who involved in scheduled business of a certain scale have not much choice any longer.