I spent university years designing and printing out circuit boards. At school, I created circuits via ‘etching’ - hand drawn in pen onto copper before dropping them into an acid bath.
Over the last few years, I’ve found Bare Conductive's work inspiring. They have been very clever with their development of creative kits and tutorials, such as the twinkling christmas tree, glowing houses or flashing greetings cards.
Here’s another conductive pen that allows you to draw circuits smudge free with a ball point pen - Circuit Scribe. They have just launched a new Kickstarter.