I have written about trackballs before. They are better for me than mice, unless I've been really slaving away. In which case, I need to resort to using a backup mouse to stave off repetitive stress injury. Happens once or twice a year.
All together, I have four trackballs in current use. Two are Logitech TrackMan Wheel devices. You can find them around for about 30 bucks. They are small and use a thumb-manipulated ball to move the cursor. They have a wheel between the two buttons. One goes on the laptop computer, the other on my second desktop. That's the one I use to read documentation and do some background tasks. It has a 22-inch Dell monitor, running in portrait mode (1200x1600).
The TrackMan Wheel devices are small. Maybe too small. It makes for a great trackball for the laptop, easy to include in the paraphernalia that I shove in the laptop case. But the device feels a little flimsy and I have never really been happy with it on the desktop if I have to use it a lot. But it does have a scroll wheel, which is REAL IMPORTANT these days. And truly it takes up very little desktop real estate (I'm talking about the hardwood desktop, not the Windows desktop).
My bedroom computer is merely a web browsing, Pzizz-playing machine these days. It's an old computer, running Win2000 with not much else but Firefox, Pzizz and a connection to the rest of the network. Pzizz is a sleep aid program, and I use it for afternoon power naps. The trackball on this machine is an original Logitech TrackMan Marble. Of course, you can't buy it retail these days, although you CAN find it for about 30 bucks on eBay. It's huge, heavy and a joy to use. Big ball that can be moved around by fingers OR thumb. Lots of buttons ... but no scroll wheel. And in today's Firefox universe, that's a no-no! I'd use it for the doc-viewer machine in a heartbeat, if it had that scroll wheel.
It must be obvious I like Logitech devices. Even my emergency mouse is a Logitech device. But there's a surprise coming for the trackball I use on my main machine.
I use a Microsoft Trackball Explorer! Yep, a Microsoft product! How's THAT for Microsoft bashing. But here's the catch. Microsoft discontinued the product. Once again, you have to head for eBay! The once-40 buck product, now fetches 75-200 dollars!
It's not quite so heavy as the TrackMan, but it's got decent heft. The ball is a big one, manipulated by the fingers. It can right and left button click with the thumb, and has a very good scroll wheel between those two thumb buttons. It also has two rarely-used buttons under my ring and little fingers.
About the worst thing I can say about the Trackball Explorer is that the software for setting it up runs close to 50Megs in size. I find that ridiculous, but it isn't like the Logitech mouse drivers are all that skinny either.
All in all, I heartily recommend trackballs. I hope you get lucky on eBay.