jimusic
That's the second suggestion I've got for the Kensington track ball.
 
Is that the one you have as well Dave, or the Logitech one I haven't opened yet?

I have the Logitech.  I used to have a Microsoft trackball and that was my favorite but it's no longer manufactured.
 

I think I'm gonna go for the Kensington one, whereby I can use it with either hand - and place it where convenient as well, as I'm also limited in space to move the mouse.
 
Thanks for all the replies Buds.

I dont use a trackball, but using a Logitech Touchpad for the same reason as several here: both space and wrist issues. 
 
Looks about like this: 
http://www.logitech.com/en-us/product/touchpad-t650?crid=1153
 

kristoffer
I dont use a trackball, but using a Logitech Touchpad for the same reason as several here: both space and wrist issues. 
 
Looks about like this: 
http://www.logitech.com/en-us/product/touchpad-t650?crid=1153
 

I actually have the version one down from that one as well.  
I should spend some more time fiddlin' with it. 

Another endorsement for trackballs.  I originally bought one to use with my laptop (non musical stuff) so that I didn't have to find a flat space to move a mouse around on (I hate the touchpads on laptops).  I like it so much that I swapped out my mouse on my sonar rig for one, too.
 
I use the logitech one.

I use Kensington trackballs, but not the super duper one mentioned above.  I use an Orbit http://www.kensington.com/us/us/4493/K72337US/orbit%E2%84%A2-trackball-with-scroll-ring for my studio desk and an Orbit wireless http://www.kensington.com/us/us/4493/K72352US/orbit%E2%84%A2-wireless-mobile-trackball for my mobile laptop studio.  Both have a scrolling ring feature; the wired has a tactile ring like the Expert model and the wireless has a touch ring that you swipe for scrolling.  Both also have lock scrolling (for scrolling with the ball) when both buttons are pressed simultaneously.  I like the orbit over the expert simply because it takes less desk space.
 
As for logitech's trackballs, I've used them but they are ackward (thumb ball), bulky and not comfortable to me.  The design seems to make ergonomic sense, but isn't practical in use.  My thumb just doesn't have the same "throw" as my fingers.
 
Kind regards,
 
Living Room Rocker

This felt really awkward for the first few days. Now I love it.

Jeff Evans
I use a Kensington trackball in conjuntion with the mouse.  I feel both are required.  One of the things I really like about the trackball is the outer ring that surrounds the ball itself. When you get into any browser it makes scrolling a dream and much faster.
 
They are not for everyone. I like it though. There are some operations that you can do rather smothly with the trackball compared to the mouse.  It is important to be able to use the left and right click buttons with one hand while you are also using the ball.
 
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Some people swear by trackballs, other people hate them. Maybe it has something to do with the size and shape of your hand. I used one for a while a few years ago and loved it initially, then after one particularly epic Photoshop/Lightroom session I realized that my hand hurt like buggery. It was all seized up. I trashed the trackball the next day and went back to a regular mouse. 
 
Another option of course is the vertical mouse, these are (purportedly) good if you have tendon problems as they force the arm and wrist into a less damaging position. I used to know a woman with crippling tendinitis and she swore by hers. 

sharke
...Another option of course is the vertical mouse, these are (purportedly) good if you have tendon problems as they force the arm and wrist into a less damaging position. I used to know a woman with crippling tendinitis and she swore by hers... 

Hmmm. I've not heard of a vertical mouse. I'm curious though. 
 
Any links there, sharkey?