If you're taking on a home improvement project that requires a little bit of wiring and other electrical know-how, it can be a daunting—and dangerous—task.
Well the next best thing to having an electrician help you every step of the way is to have this "Made by a DIYer for DIYers" iPhone application in your palm: Electrical Ref.
Have you ever wondered how many Ohms that resistor your holding is? Maybe wondered what the capacitance is of a ceramic disc capacitor with the code 103? Forgotten how to assemble a 555 timer circuit? Or wondered how to make your Arduino detect an EMF? Then Electrical Ref is the app for you. It features a resistor calculator, capacitor calculator, & circuit diagrams.
Here's a link to iTunes if you'd like to pick up this DIY Electrical helper for $1.