The Logitech M705.
A couple years ago I found myself in need of a basic 3-button mouse for use with 3d modeling applications. Wireless mice are nice, but I was getting tired of constantly changing the batteries every month. So when I came across this one which Logitech boasts as having a 3 year battery life at under $40, I decided to give it a shot. Well here I am over 2 years later and I am very pleased to report that it is still showing a remaining charge of 80%! I have never changed the batteries since the day I opened it.