Calculators (especially graphing calculators) tend to function like tiny computers. Not like the kind most people are used to, no these are usually a lot "weaker" than those. But a simpler computer is my type of computer.
The Ti-84 Plus is my calc of choice, with a large library of software and a handful of languages to chose from for programming, it's a comfy device. It runs off 4 AAA batteries, and has a quite small monochrome screen.