Pspice
http://www.ee.washington.edu/circuit_archive/software/
http://margo.student.utwente.nl/el/cad-cam/spice6w1.zip
http://www.willingham2.freeserve.co.uk/winspice.html
Cadence Software, formerly Orcad, Microsim.
http://www.cadence.com/
SPICE based analog circuit simulator
http://www.newburytech.co.uk/
electronics circuit simulation
http://www.spectrum-soft.com/
http://margo.student.utwente.nl/el/cad-cam/spice6w2.zip
Versions 5.3, 8.0, and 9.1 available for download.
http://www.engr.uky.edu/~cathey/pspice061301.html