Thank you for this links, iphigenie!
Funny enough i am on the hunt for an trackball-mouse too,
i never know that there are such things like you show us.
(Funny, but i don't thing that they are nifty, they looks like they would disturbs me)
I was in the last days in two big computer stores in GER and i saw a lot of mouses in all colors, but only one Trackball between them.
I think i go buy one at eBay.
I have had an trackball with my AMIGA and later i bought one for my PC, but this is broken now.
Then i used a simple mouse with scroll wheel (which i miss on all PCs i came along and they didn't have this wheel)
but i miss this simpleness to let the ball roll -- just with a quickly stroke of my finger -- and the cursor move across over the screen.