I use exclusively Microsoft Intellimouse Explorer mice (the big silver ones) as I have hugely long fingers. I have used trackballs in the past, but I'm with DAna, they cause my wrist and thumb to lock because I have long thumbs also and the movement is actually quite uncomfortable.

Only other Mice I use are my Amiga Technologies Mice (one black, one white) and my token teardrop ADB mouse for the older Macs.