Rafael found an application called Yenka in the web. This software is wonderful! You could use it for simulating many things. We are using it for designing and simulating electronic circuits but other stuff like mathematics and physics are available too. It is a very nice application for teaching and learning...
Below is an image of a simple transistor switch designed with Yenka.
You could simulate the circuit. When switching the button in the lower left corner. You could measure the Voltage and Ampere at every point of the circuit... ;) Now I don't need so much time to solder anymore... even it is a lot of fun soldering own devices.
You could download it for free and use it completely for free when using it at home! With all features!!! There is a version for Mac, Windows AND Linux available.
I got this great book yesterday: "Make: Electronics". It was exactly what I needed. It describes in a very hackish way how electronics works...
I got the german translation and read a lot in it within the first day. It has many examples of analog circuits for building funny and useful stuff by yourself. DIY!
Thank you very much for this book! I love it!
I found this nice Android app today. Since I am setting up the monitoring of some servers using Nagios this app is very useful to me. The app is called Nagroid and it is completely free and the code is available at Google Code.