Finite Size Scaling and ``perfect'' actions: the three dimensional Ising   model
  Using Finite-Size Scaling techniques, we numerically show that the first irrelevant operator of the lattice $\lambda\phi^4$ theory in three dimensions is (within errors) completely decoupled at $\lambda=1.0$. This interesting result also holds in the Thermodynamical Limit, where the renormalized coupling constant shows an extraordinary reduction of the scaling-corrections when compared with the Ising model. It is argued that Finite-Size Scaling analysis can be a competitive method for finding improved actions. 
H. G. Ballesteros, L. A. Fernandez, V. Martin-Mayor, A. Munoz-Sudupe