Circuit Simulator!

[Frank_NH]

Check out this *free* Java applet:  

Circuit Simulator

It simulates analog circuits in a real time environment.  You can add/remove components on the fly, build up your own circuits, and there is a huge library of basic circuits.  DC and AC input/output.  O-scope type probing.  It's a wonderful learning tool!  

Below is one of the canned examples of a non-inverting op amp, showing an AC voltage gain of 3 (Gain = 1+Rf/Ri = 1+2k/1k = 3).

[rocket88]

Awesome find man. Going to use this when I get home for a project.

[motterpaul]

Frank - I saw some people posting about LT Spice - is this like that? Seems to be the same thing though I have not used either.