Not the first game-centric mouse to offer on-the-fly sensitivity adjustment, but the first to come from a company with first rate QA and globally recognized staying power. In fact, the Logitech MX518 Gaming-Grade Optical mouse is pretty much the quintessential PC gamer's peripheral--and will probably remain so until someone comes up with a directly-to-cerebral-cortex interface device.

Basically the MX518 is the evolution of the MX510, Logitech's previous high performance, high speed mouse for gamers--conventional power users, too, for that matter. Most notable in a first-person shooter game environment (and RTS games requiring a quick grouping of units), it allows you to switch the optical reader resolution between 400, 800 and a dazzling 1600dpi (by default; custom resolution configurations also available), while playing, with a mere tap on its smartly placed buttons in front and back of the scroll wheel. This means you can control the speed at which you reticule/gun site moves about on screen, giving you adaptive precision as the situations change from wide open outdoors, tight and confining indoors or toggle-zoomed through an otherwise un-steady sniper scope. It's the edge you've been looking for.

There are additional customizable buttons too, which can take the place of any number of in-game keystrokes, macros, binds or what-have-you. As good as a mouse can get.