The Scrollpoint mouse by IBM/Lenovo is easily the best engineered mouse I've ever had the pleasure to use. It ingeniously combines the mouse and pointing-stick, utilizing each of them in the area they're best suited for; the mouse for fine cursor control and the pointing-stick for quick and direct scrolling.
Previously I owned a Mighty Mouse by Apple, but grew frustrated with the scroll-ball getting clogged. It seemed pretty ridiculous to me that after eliminating balls from underneath a mouse, that I'd be subjected to the same problems when they were moved to the top. Scroll wheels are better, but can't handle side-to-side very well and for scrolling through a long document requires the user to lift their finger up again and again. A touch-stick on a mouse seemed like a great idea and I was pleasantly surprised that IBM actually made one.
The Scrollpoint has most of the typical features one would expect on a mouse. It's an optical, 3-button mouse, that plugs into a USB port (or PS/2 with included adapter). The pointing-stick on the current mouse (the one in the picture is a previous model) has a plastic bar rather than the traditional nub which works better for it's particular application. No matter how long a document is, you never need to lift your finger off the point-stick.
I've had my Scrollpoint for about 6 months so far and might even pick up another one to use at work. I highly recommend it. Priced at about $25, it's inexpensive enough for you to give it a try.