The latest indie game dev Humble Bundle includes ProMotion, which is also a great pixel art editor and animator.
And it gets you a copy of Spriter, and Sprite Lamp to light your sprites. And loads of assets.
For drawing pixel art "on the go", try Pixly (which is free, and frankly quite amazing):
https://play.google.com/store/apps/deta ... ixly&hl=en