JavaScript Calculator
I remember using the TI-108 in elementary school. The teacher had a big box of these calculators, which were only made available for special math assignments. Well, now you can enjoy the patriotic color scheme of this classroom classic whenever the mood strikes!
Nifty feature: Because we have the benefit of using this TI-108 in a powerful modern browser, the font-size of the screen will automatically decrement to accommodate as many digits as are required. (So there's no pesky truncation of long numbers.)