I've used Trackballs for years. First one I bought was a Genius cost about $250-$300. Worked very well till the steel roller was no longer round, had a flat spot worn into it by the plastic ball. Bought the next generation of the Genius trackball, what a heap of junk.
Bought two MS IR trackballs 1 x Trackball Explorer and the other was a std MS trackball. both have 4 buttons and 1 scroll wheel. You roll the ball on the explorer with your index and/or middle finger, click the left and right buttons and operate the scoll wheel with your thumb, use whats left on the other two buttons. I nearly sent this TB back, just couldn't get used to it but after about 1 month found it to be very good. With the MS TB you roll the ball with your thumb and buttons are used with fingers. I found it good to have the change of operation between work and home. Get to use the tendons a little differentley.
The TB at work crapped out the other day
(steel got worn out by plastic again) so I put a std ms optical mouse on there, it works ok but I got to much crap on my desk to find room for it to move.
Think I'll go looking for another MSTB
6 months ago I got a WACOM INTUOS 3 A4 Tablet. Great for graphics work, touching up photos etc. The pen (cordless) takes some getting the hang of. I have dual LCD's 1 x 19" 1280x1024 ( just got it last week) 1 x 17" 1280x1024. The Intuos A4 surface is the total area of the extended desk top. If you are working on the right hand screen thats the side of the Intuos you are working on with the std pen, if you maximized then you must reach to the far right corner to minimize. BUT I bought the Wacom 4 button with scoll wheel mouse. It works like a mouse(of course it does... it's a mouse). Cordless
Don't like the Wacom mouse with Sketchup.
P.S. Just a note on the 19" Philips LCD. I wasn't going to get a 19" till the price of the higher res monitors dropped. The eyes an't as good as they used to be and I decided the 1280x1024 would make things easier to find. Have you noticed when we were using CRT's we had them a lot closer then we do LCD's. I can see my new LCD ':D'