I have two ball mice I still use:
The first one is a serial mouse, which I use for my old-school 486 DX/2 system. Believe me, I tried using an optical with it: no go.
The second is an average two-button mouse... except it's also a phone!!! Seriously. It has the keypad in a little recessed section of the mouse, covered by a hinged lid. There's a plug for a headset at a little box attached to the cord, where the phone plugs in as well. If it wasn't for the fact that the cord is too short I'd use it for a lot more stuff.
On a related topic, there used to be micro-mice you could buy for fairly cheap with the most useful mouse balls ever. The reason: they were the exact same size as paintballs. Ouchies!