This is a Windows only tip, so I’ve not played much with it. However, Embrio does look like a perfect experimentation kit. Take an Arduino, connect your peripherals and draw the solution. It even lets you work in a live mode, getting immediate feedback to your changes.
The whole embrio site is filled with tutorials for common setups. For instance, how to use a breadboard, buttons distance sensors, servos, PWM and more. There are also examples combining these skills into large projects.
The basic version is free, while a perpetual license with all features unlocked costs USD 50.
Via dangerousprototypes.