Mine was a Casio fx-something. Teachers didn't like it but it didn't let me cheat and it was just the right amount of functionality to help me with math. Carried me through Pre-Cal, Trig, Calculus and Differential Equations.

That was my first graphing calculator in high school, because it was way cheaper than the equivalent TI. Like seriously 1/4 the price for "beginning of the school year" sales.

That thing was fine, and if I hadn't dropped it and broken it, I probably would have kept using it for the rest of high school. I eventually replaced it with an HP.