Sure, there are some excellent calculators in the Android Market, but do any of them make you hesitate for a minute when looking at them to figure out whether you are staring at a phone or a smaller version of your favorite Texas Instruments machine? Doug Melton's ports of the popular AlmostReal TI-83, TI-85, and TI-86 emulators to Android are so successful, most of your professors wouldn't even know the difference if they saw one of these on your desk. The buttons, the layout, the graphics, TI-BASIC program support - it's all there. Awesome.
I'm not sure whether Texas Instruments goes after emulators of its calculators, but I would download these ASAP if I were you.