Great piece of software everyone should have

[stecykmi]

PSPICE! Get the free "student version" here: http://www.engr.uky.edu/~cathey/pspice061301.html

Student version has no locked features or anything, it's basically the complete version. I personally use V9.1 and haven't tried the earlier versions. Install "Schematic", that's what gives you the fancy graphic interface.

Anyway, PSPICE is circuit simulation software that is great for designing or learning about circuits. There is some learning curve, but I've gotten fairly okay at in the past two years so I'd be happy to answer what questions I can about it. There are also many tutorials online that can be found with Google (many of them from engineering courses, if that's any indication of how pro this software is). One of the trickier parts is setting up reasonable simulations (hint: frequency sweep and transient analysis are the ones that I've found most useful for audio design). Once you've figured it out, it's a breeze to find the frequency response of an amplifier.

I've gained so much of a better intuitive grasp of electronics through messing around with PSPICE than any engineering class I've ever taken.

On a historical note, the software, at it's core, is a differential equation solver. Having a computer program that was able to quickly solve the equations for a circuit was a huge step forward for electronics design, but the original SPICE software (circa 1975) had no graphic interface, you'd have to input the entire circuit by what was connected to specific nodes.

[aziltz]

5spice is another version of this.  it features a different GUI, but it also sports a free version.

[bigmufffuzzwizz]

Is this similiar to MultiSim? Thats what I used in class and thinking I really need to get myself a copy now.

[stecykmi]

never used multisim but a cursory glance suggests so.

[bigmufffuzzwizz]

This appears to be of great value and I wanna say thanks for sharing this!
When I get started with it I'll definitely come to you with any questions 

[k.rock!]

Aaaahh...PSPICE...what lovely memories of college (2 years ago haha) This along with LabView, SolidWorks, MatLab and AutoCad just made my days!! Awesome software to have...

-Kaleb