HP (Hewlett-Packard) 50G Graphing Calculator
A little nicer aesthetically than the TIcalculators, the HP50g offers a computer algebra system and has great performance at a low price. It uses a 75 MHz ARM9 processor and can be hooked up via USB. It even has an SDslot. Standard plotting functions such as 2D, parametric, and polar are supported, along with differential equation plotting. The computer algebra system is a huge plus of this calculator versus others. Unfortunately it is prohibited on the ACT test. It's not as popular as the TI-84, but more functional and cheaper. Many may opt for the TI-84 instead due to its popularity and test acceptance. The HP 50g's symbolic derivative and integral capability might come in handy for calculus, though. It supports more obscure reverse Polish notation (RPN) as well, so if your old-timer parents want to use it, you're in luck!