I was playing around with a sun-tracker idea (arduino operated, of course) a couple months back, but seeing as the project flopped, I made the best of a bad situation and derived an interesting geometrical equation for a sunflower-esque geometrical shape (well, the equation solves for one side, but the rest is either given or irrelevant when constructing the model in real life):

http://www.rustechstudio.com/etcetera/geometric-sunflower/

…and yes I am sneakily promoting my blog instead of reposting the whole article here