For power electronics, I would recommend LTspice/SwitcherCAD which is free and full featured without any node limitations. Check it out at Linear Technology - Design Simulation and Device Models The simulator is very fast and optimized for power electronics. Most of the power supply ICs that Linear Technology makes is also included with the distribution of the software and is used in example circuits. Nearly all major power electronics topologies are covered so you can have an example simulation running in a few seconds. This software is definitely worth a look.
Best regards,
\[v_c\]
P.S. I don't work for Linear and the opinions expressed are based on my experience working with many simulators from a student's point of view.