I really like this piece. The Archimedes Spiral can be a mathematical compositonal tool. It's also just a damn spiral and I love spirals.

This was done in colored pencils. :3

Edit: There are other cool spirals, such as the one used in Divine Proportions, the Golden Spiral. which is a kind of Logarithmic spiral. L. Spirals are found all over the place in nature, as are most fractal type things. I don't pretend to understand all the mathematics behind them nor all their uses, but I do find them fascinating.