QUCS is a pretty awesome tool considering the price :)

I didn't realize that QUCS-S did EM simulation (section 3.1.6.2 in this article) and I'm curious what the features/limitations are. The killer feature in a tool like this for signal integrity applications would be support for IBIS or IBIS-AMI models for time donation simulation... There's a great FOSS simulator for AMI but it's not integrated with a schematic environment.

Considering how slowly EDA/simulation tools move combined with their insane cost, it's an area that's certainly ready for a FOSS tool to move in the way software tools have gone.