Logitech MX518 - 17 years old last month.

I ordered this mouse on December 23rd, 2005. It's been with me through full time raiding in WoW (twice!), school, six moves, three states, and being work from home for the last 7 years. I use it for my work and for my home PC and refuse to get a new one until it dies. I just had to clean it out for the second time as the scroll wheel wasn't responsive.

It still works pretty much as good as new!