I have been obsessed with Adobe Ideas on iPad. It is a simple vector based sketchbook app. Because it's a vector app you can enlarge or shrink your art to any size without losing quality. Here is a quick overview of the art section of the app.
(the move tool is under the hand tool)
What I usually do is take a picture of my art from my sketchbook, put it on the photo layer and then trace over it. You can adjust the opacity of the individual layers so I tend to make the photo layer lighter. Then I start creating shapes. As long as the shape is closed I can fill it with color.
You can have up to 10 layers and upload the drawing through Creative Cloud into Illustrator; layers and all. You can edit and tweak your creation in Ai. I have discovered some annoyances though. If you have a transparent layer you can't make it opaque and lines are a pain adjust. I'm still learning Ai but I believe the the lines you make with Ideas behave like the Blob Brush in Ai. There are lots of anchor points on the line so manipulating them is difficult. The eraser tool works pretty well on the lines though.
Here are some other things I've created.
Thanks for stopping by.