EE Times has enlisted its readers to say which free circuit simulators they use. I saw that a number of people like PSPICE which is not free. LTspice was another favorite. The number one complaint was the lack of device models. PSPICE is a great tool with plenty of models. It would be cool if was open source. It would seem that online circuit simulators like CircuitLab is being used by students at hundreds of universities around the world so programs like PSPICE, LTspices, and Multisim are likely to fad away.