When talking about customizing a toy, designer toys would be the way to go. I came across this cute Monkey looking DIY over at LE LAB.
I like the design as it was very monkey like but most of all it has a flat face for noob like me for easy to draw on. It has various joints on the head, arms and it's long curvy tail.
Here are some custom design on that DIY design
Head over to Le Lab to view more designs.