If you need a 3-D field solver, you might want to give Simbeor (http://www.simberian.com/) a try. This year it again won the Design Con Design Vision Award (it was the 2010 winner, too).

A big plus for me is that Simbeor results have been verified against measurement of actual hardware (you can get details on this from the Siberian website).

Some 3-D solvers can be very difficult to properly use, especially if you don't build models with them daily. The special tricks required to correctly assign ports or to set boundary conditions are easy to forget unless you use the tool enough to become truly expert.

In contrast, I've found it easy to build 3D transmission line and via models in Simbeor, even when I haven't used it for a while. The tutorials are excellent, and the website has a very nice collection of technically useful white papers (several of which I reference in "Understanding Signal Integrity").

This is a great tool for designing serial channels, designing vias, and analyzing the electrical behavior of interconnect (including, but not only, very high-performance interconnect). The website is worth checking out: It's a good resource for those wishing to learn about the electrical characteristics of high-performance serial signaling.