According to your request for friendly Magnetic field calculator software, I would recommend you Comsol multiphysics. You can simulate and calculate both Static and Dynamic magnetic fields. There are several parts in the Magnetic field section that you can choose the appropriate module based on your physics.
The interesting point is that you can determine the shape and size of the Magnet and investigate the different features of the magnetic field. You ought to check the Comsol multiphysics Help to reach more helpful information and examples.(the help icon is at the top and right corner of the screen)
I have contacted my co-worker and he recommended me to use getdp, which you can find on the site http://www.geuz.org/getdp/ .It can be used for 2d and 3d calculations. It takes a little effort to learn, but it works really well and is free AND available for Windows/Mac/Linux.