http://hackedgadgets.com/2007/04/28/computer-mouse-using-a-dead-mouse/
http://www.instructables.com/id/Mouse-Mouse!/
less disgusting but just as innovative:
http://www.geekologie.com/2008/01/boy_builds_bicycle_entirely_ou.php
I has found this via "mouse (http://icanhascheezburger.com/2007/07/20/scuze-meeh/)" image search that also found LOLmouse (http://icanhascheezburger.com/category/lolmouse/).