I get asked this question a lot. Fortunately the answer is simple.
I use a Wacom Cintiq Companion Hybrid (32GB) connected to a 5 year old MacBook Pro. I use a couple of different programs but my favorites right now are Autodesk's Sketchbook Pro (the subscribed version) and Adobe's Photoshop and Illustrator (CS5).
The combination of these pieces has really opened up a whole new world of art creation. I used to use a LOT of paper and colored pencils. Now everything I need is combined in a neat, easy to use and share format.