If you want to pay look at TINA. TINA is very good and highly recommended. You could also look at the free demo version but I cannot comment on the limitations.
You can get a free 30-day evaluation to see how it goes, but will need to purchase a license thereafter. If you are a student there may be student deals but I do not know what they would be. MultiSim has been recommended by several members on here before.
I have been working on a simulation package. It is now in a reasonable shape (includes a GUI, etc). You may take a look: www.ee.iitb.ac.in/~sequel
There are two ppt files there, one with electronics examples, and the other with power electronics examples. All examples shown in the ppt files are available as project files when you download the package.