Procreate by Savage Interactive is the best power-drawing and painting tool I've used on the iPad and it's just hit version 2. Included in the update is 64-bit support for iPhone 5s, iPad Air, and Retina iPad mini, as well as an all new, all iOS 7 icon and design. There's also an improved gallery, and even better - new GPU-acclerated filters like Gaussian Blur, Sharpen, Noise, Hue, saturation & brightness, Color Balance (Highlights, Midtones, Shadows), and Curves (Gamma, Red, Green, Blue).
Grab your finger, or a stylus, and get ready to get your art on. If you already own Procreate, the update is free, and if you don't, it's the best money you'll spend on supplies all year.