This is a pretty old, plain TI-89 calculator that took me through both High School and my electrical engineering degree. It's got a mark on the main screen and the back was engraved with my name. It still works great.
This calculator may be special, however, because I have an Erdős number of 3, to which I attribute this calculators' supernatural powers. While the abilities of this calculator are indeed stunning, I feel that I am currently not worthy and must let someone who is truly capable of understanding its true powers have it.