Sketchbook Pro App
Autodesk's Sketchbook Pro is a professional desktop painting and illustration app available for Windows and Apple computers. Unlike the mobile versions, the desktop version allows greater control over resolution and canvas size/shape which is essential if you want to be creating for print. Running Sketchbook Pro on my Surface Pro is a dream combination especially with the pressure sensitive Surface Pen.
Here are a few examples of work I've produced with Sketchbook Pro
I wanted to see how detailed I could work on the Surface Pro, so I started this canvas, which was 80x50cm, 200dpi. The final file was pushing 100MB, with no lag. This on a portable tablet is incredible.