Hi there,

as regards symbolic anaysis, a very nice program is Analog Insydes www.analog-insydes.de
It bases on Mathematica, uses the operating point and device model from your favorite network simulation tool. You can simplify equations by automatically leaving out terms and thus, get the question "how does my circuit operate" answered (instead of "how does my circuit behave" which is answered by network simulation programs).
- achim