All-Purpose Numerical Evaluation of One-Loop Multi-Leg Feynman Diagrams
  A detailed investigation is presented of a set of algorithms which form the basis for a fast and reliable numerical integration of one-loop multi-leg (up to six) Feynman diagrams, with special attention to the behavior around (possibly) singular points in phase space. No particular restriction is imposed on kinematics, and complex masses (poles) are allowed. 
A. Ferroglia, G. Passarino, M. Passera and S. Uccirati