2- or 3-button trackballs for Mac PowerBook?

[Dan Kalikow]

Hi -- newbie to the group, here, first-time-posting via Imdat Solak's 
"Halime" newsreader.  I'm using GNU Emacs (powerpc-apple-darwin6.2.2) - 
Andrew Choi's port to OS X - on a Titanium PowerBook G4 1Meg machine.  
The "touch- pad and single-clicker" is OK for most stuff but I'm finding 
the lack of a  "real" mouse for emacs kinda restrictive.  Looking for 
your thoughts (or  pointer to good places where such thoughts are 
collected?) about which  USB trackballs are good for xemacs.  I know 
that 3-button trackballs  exist, and I hear that emacs can deal with 
them smoothly on the Mac.  Smallish size  of the trackball is kinda 
important -- I don't want too large a wart on  the side of my PB while 
editing.  Whaddayathink?