Just wanted to include this excellent illustration of Euler's formula
(it really deserves to be shown here in its own right and not just as a link in one of the comments):

alt text http://upload.wikimedia.org/wikipedia/commons/e/e3/Euler%27s_Formula_c.png

Source: http://en.wikipedia.org/wiki/Euler_formula

Just wanted to include this excellent illustration of Euler's formula
(it really deserves to be shown here in its own right and not just as a link in one of the comments):

Source: http://en.wikipedia.org/wiki/Euler_formula