SPICE is program that simulates electronic circuits on your PC. You can view any voltage or current waveform in your circuit. SPICE calculates these voltages and currents versus time (Transient Analysis) or versus frequency (AC Analysis). Most SPICE programs also perform other analysis like DC, Sensitivity, Noise and Distortion.

http://www.ecircuitcenter.com/AboutSPICE.htm

Get the free SPICE software from here:
http://www.linear.com/designtools/softwareRegistration.jsp

Discover Circuits, with its 23,000+ electronic circuits or electronic schematics cross-referenced into 500+ categories, is a vital resource for engineers, hobbyists, inventors & consultants. The site's collection of links will help you find quick solutions for electronic design problems.

Get them at http://www.discovercircuits.com/list.htm