"Circuit Maker" is one of the many circuit simulators you can find.
It' s good enough and it is usually used with his "brother" Trax Maker, that is a layout software.
A negative aspect is that you must pay to have it, (or download it from e-mule, of course ;D) .
There are a lot of free circuit simulators, made by electronic IC producers who give the software to simulate their products; anyway you can use them as general purpose simulators.
Try This
http://www.linear.com/designtools/softwareRegistration.jsp
