Have you tried live painting? You could scan in a hand-drawn image, ink it with the pen, and then color it with the live paint tool. It works really well. :D
The image I attached was done all in illustrator with the live paint and pen tools, in about 10 minutes. ( The eyes were what I put the most effort into, the mouth is horrible. XD ) Live Paint's really nice if you want some simple artwork with coloring, without using a tablet. The gradients are a bit tougher to use than in Photoshop, though; the interface is a lot different.
Also, like LightningEagle said, you're pretty good at doing perspective with those eyes. They look great. :D