I prefer a real
wired mouse like this:
I am using this mouse right now and love it for its comfortable feel, variable speed vertical scrolling, side scrolling and the forward/backward buttons. And it is compatible with Windows XP/Vista/7 and MacOS X 10.5/10.6, too.
Apple tried to be "too cute" with the new Magic Mouse and it's nowhere as good as the Logitech M500 if you want to do real
work on your iMac or Mac Pro.