Two-dimensional (2D) electrical imaging surveys are now widely used to map areas of moderately complex geology where conventional 1D resistivity sounding surveys are inadequate. The RES2DINV program uses the smoothness-constrained least-squares method inversion technique (Sasaki 1992) to produce a 2D model of the subsurface from the apparent resistivity data. It is completely automatic and the user does not even have to supply a starting model. On a Pentium based microcomputer, the inversion of a single pseudosection is usually completed within minutes. It supports the Wenner (α,β,γ),  Schlumberger, pole-pole, pole-dipole, inline and equatorial dipole-dipole, and non-conventional arrays.
You can download a semi-demo version for test and evaluation.