When the Mac was first introduced, its mouse separated it from all the computers that came before it, and those that came after it, for a long time. Until Windows and other platforms adopted the mouse as one of their primary input devices, the Mac and its mouse really stood out from the crowd. Now, the default Mac mouse stands out, but not in a good way because Mac users would really benefit from having more than one button so they don't have to use two hands to open contextual menus or perform many other actions. All other platforms come with at least a two-button mouse, and most mice also include a scroll wheel.
All desktop Macs come with the Apple Pro Mouse. This is an optical mouse, which means it uses light to translate your movements into input information (as opposed to the rolling ball in previous generations of mouse devices). The Apple Pro Mouse uses the entire top half as its “button,” which makes using it even easier (if that is even possible). And it shares the same clear or white plastic look as the Apple Pro Keyboard. If you are happy with the standard Apple mouse, you don't need to worry about replacing it with something else.