Almost every personal computer that's sold today comes with a mouse -- but that hasn't stopped companies from developing mice with appearances and features as unique as the people using them.

The standard mouse that comes with many computers is pretty vanilla -- a pointing device with two buttons and a rolling ball. Today's after-market mice offer extras that make computing easier, such as a wheel for up-and-down scrolling through a document or extra buttons that launch computer programs.

Take, for example, Apple's new Mighty Mouse ($49, Mac OS X v10.4 or higher), which ended Apple's longstanding adherence to single-button simplicity over versatility.

The ambidextrous Mighty Mouse has five buttons, though the right and left ones are not visible as buttons. Pressing on the left side of the lozenge-shaped mouse body works like the original Mac mouse button, while pressing on the right side can bring up a menu of choices -- just like the right-click functionality on a Windows PC.

The tiny scroll ball easily and comfortably scrolls documents not just up and down, but left and right, as well -- useful for spreadsheets, graphics, and Web pages that are too wide to fit in the browser window.

Press the scroll ball and Apple's Dashboard feature (available in OS X Tiger) appears onscreen, allowing instant access to searches, contacts, and real-time data such as weather or stock quotes. Squeeze the side buttons and the screen shows miniature images of all active programs. But squeezing takes some getting used to because it offers no tactile feedback and requires significant pressure. Similarly, too light a touch can make the scroll ball turn without actually engaging and scrolling the page.

Like most after-market mice, the Mighty Mouse uses an optical sensor that tracks over most surfaces (even a pants leg -- useful for laptop users) and ends the hassle of roller ball gunk. But even on the fastest setting the mouse pointer still felt slow -- a problem not evident with non-Apple mice running on a Mac. The Mighty Mouse has no Windows drivers, but its basic features worked on a PC running Windows XP -- without the horizontal scrolling.

Still, there are plenty of mice on the market that have been designed for Windows PCs.

Microsoft's Laser Mouse 6000 ($65) and Logitech's MX 610 Laser Cordless mouse ($60) each replace the optical LED found in the Apple's Mighty Mouse with a laser that works on surfaces that normally defeat the optical sensor, such as glass.

We even got the laser to track over the screen of a computer monitor. Lasers make these mice far more precise, though the extra precision is useful (and noticeable) mostly to graphic artists and hard-core gamers.

Microsoft's mouse has an ambidextrous shape and special features such as a magnification mode.

But it also has its quirks. Like other Microsoft mice, the 6000 won't install if you don't let it remove existing mouse software. This is a real problem if your other pointing device is a trackpad on a laptop.

Logitech has solved this problem, allowing both the 610's control software and a standard trackpad control panel to peacefully coexist.

The 610 is not merely an input device. Two lights inform you when you have a new e-mail or instant message, though the programs they work with are limited -- no AOL or Eudora.

The cordless mouse also powers on and off when the PC powers up and down to preserve its battery. And the wireless transmitter automatically changes frequencies to overcome interference.

Its contoured shape is the most agreeable of the three, but only for the right-handed.

Logitech's mouse is the best overall mouse, especially for right-handed users who want to go wireless. Microsoft's is best for lefties and those who don't want to replace batteries. And Apple's Mighty Mouse is really only for die-hard fans of the first Mac optical mouse who thought it had too few buttons.

Microsoft's Laser Mouse 6000, left, has magnification; Logitech's MX 610 Laser Cordless flags e-mail; Apple's Mighty Mouse uses five "buttons."