High-precision estimates of critical quantities by means of improved   Hamiltonians
  Three-dimensional spin models of the Ising and XY universality classes are studied by a combination of high-temperature expansions and Monte Carlo simulations applied to improved Hamiltonians. The critical exponents and the critical equation of state are determined to very high precision. 
M. Campostrini, M. Hasenbusch, A. Pelissetto, P. Rossi and E. Vicari