Microsoft Intellimouse Explorer (1999)

 The first mainstream optical mouse earned its place on our list by eliminating one of computer technology's most pervasive annoyances: the accumulation of gunk inside a mechanical mouse. Optical mice actually existed long before Microsoft's groundbreaking product, but they were expensive and required special pads. The Intellimouse Explorer (and its simultaneously introduced siblings, the Intellimouse Optical and the Wheel Mouse Optical) brought gunk-free pointing devices to the great unwashed masses and their great unwashed desks (and laps, and armchairs, and many other places you'd never dream of using a mechanical mouse).