I'm super loyal to the Microsoft Basic mouse. It lasts forever whereas all the Logitech M100's that I've purchased (and I've purchased a lot of them) don't last more than 6 months. Sad!
+1, had a Microsoft Mouse 5000 for the last ~5 years. Good for larger hands, love the smooth scrolling having got used to it. Needs the odd teardown to remove fluff from the optical wheel sensor, I can live with that fine :)