I have used Dr. Harold Wade's PC Control Lab for Windows for my own use and for teaching loop tuning and related subjects. It is a very powerful PC simulator package that simulates one or two (for cascade, etc. applications) PID loops as well as a process with complex (and user configurable) dynamics. The screen looks like a chart recorder with the plots of the input, output, setpoint, and load moving across the screen. The user can change the mode, setpoint, output, and load and see the real time (or speed up time) response, and change the loop tuning or the process dynamics to see the change. The PID algorithm is configurable to simulate typical industrial controllers with the usual bells and whistles.
It is much more expensive than Dave St. Clair's program, but may have features you feel will be worth the price. For more information and purchase you can find it at www.isa.org. Go to bookstore and then select software, or go directly at:
http://www.isa.org/reference1/pub-dtal.cfm?T=PS&ID=RPCLABWIN&DO=0
John Shaw
www.jashaw.com