First and foremost, Eagle. It is the most awesome tool for organizing images/references. I can add multiple tags to the images and I can add a single image to many different folders!!! It's very useful if I want to have the same reference image for different projects. I can never go back to not using Eagle.

And second, my Rendr no show thru paper sketchbook! I can work with pen or even markers and if I flip the page, it's like the other side of the page wasn't even used! It's like magic!!! Working with markers in my day to day sketchbook now is so seamless! I highly recommend it.