Go to the eCircuit Center circuit collection page.
Rick Faehnrich shows some very interesting circuits with the corresponding SPICE files, explains them in detail, and suggests modifications of the simulated circuits that will help you to understand how they work. So you can at the same time learn how to use SPICE and how to design circuits. However, he assumes that you already know the basics of analog electronics. For a refresher of these basics, one place where you might look are the Basic Electronics Tutorials by Storr.
Among the SPICE files that Faehnrich discusses, many are about op amps: Op amp models, op amp basics, op amp applications, advanced op amp topics. Considering the central role that the op amp plays in the design of analog circuits, this is a good decision (for some material on op amps please take a look at my General Op Amp Books page). Other topics that are discussed include switch mode power supplys, switched capacitor circuits, audio amplifiers, control circuits, filters, sensors and instrumentation.
Although you can learn a lot about electronics by simulating and modifying these circuits, you should always keep in mind that the simulated circuit is not "the real thing". You can get important insights from a simulation, but by building the real circuit you will often discover important effects that were not modeled by the simulation. I would highly recommend that, after you have simulated and modified one of these circuits and you think you understand it, you should actually built it. Measure the performance of the real circuit and try to find where it differs from the simulation results. By doing this you will learn in which cases you can trust your simulation and when you should be suspicious. Faehnrich gives some hints on his Limitations of SPICE page.
If you are not only interested in the results of a SPICE simulation, but you are also curious to know how SPICE finds this results (and maybe you dream of designing such a simulation program yourself one day ?), you can find a short introduction on the SPICE topics page (the links under the SPICE ALGORITHM heading).
You may also be interested in some other Recommendations for Circuit Simulations with SPICE.
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