You guys are spoiled. Here's mine.
I have two dead TI graphing calculators, killed while going through engineering school: a TI-86, and a TI-89. By 'die' I mean their screens malfunctioned and the keypads became non-functional. One's screen died in the middle of my statics exam; I beat my fist against its face to get it to work, which made for a hell of a scene in the middle of a test, I assure you. I am probably the most-careful person in the world with his electronic devices, so the fact that they died within two years of purchase really made me hate TI. How many years went by before they updated or replaced the TI-86 or TI-89 models? A decade? Ridiculous, especially given that the cost to the end-user almost never changed, yet the technology in parts used became ubiquitous, if not obsolete. It was almost as if TI refused to let the early-1990s die. I found them to be non-intuitive, clunky, slow, inefficient (they go through batteries like a mofo), but worst of all they were required for a few classes.
That said, the best calculator I've ever used is my Casio from 1997-ish. I'm away from home right now, so I can't look at it and tell you what the model number is exactly, but it has a three-color screen, a teal case, and it's in the CFX-9850 series. It looks much like this one, from the Wikipedia page:
That was a great calculator, despite being a bit slow and REALLY hating cold weather. But the ubiquity of the TI units, and programs written specifically for engineering with it, pushed me to begrudgingly buy a refurbished TI-89 Titanium. Happily it has held up well, but I keep it in a zip-up padded case anyway. It seems to be much improved over the regular TI-89, and I enjoy using it as long as I don't have to bust out the manual to finger out TI's silly coding and key sequences for operations.
My short list of most commonly used calculators is as follows:
1. Excel -- much of what I do is done easiest with a spreadsheet and graphics
2. Win7 built-in calculator (whoever thought to make it do binary and hexadecimal, THANK YOU!)
3. My Android -- there is some great calculator software out there now! I use Arity, RealCalc, TechCalc, and a couple others.
7. That TI-89 Titanium