A few weeks ago I bought a great little vector drawing app for the iPad/iPhone called Assembly – Graphic design for everybody. The app has a library of vector shapes that you can scale, colour, duplicate, flip and rotate to create a design, logo or illustration. Transparency and drop shadows can also be added and there are three output options: jpg, png and sgv. The simplicity of using predetermined shapes and lines to create your artwork makes it fun and challenging to use, I like to think of it as a sketch book for vectors.
This is a quick illo created with some of the app's shapes from their special Halloween package. The first pic shows the finished illustration in Assembly.  Then, to add more drama I exported as a jpg and manipulated the file with PhotoToaster, a basic photo editor and effects app.  Happy Halloween!