We use TI-86 graphing calculators, and the software Derive, to help students visualize formulas. There's a nifty little piece of software called Cyclone that draws three-dimensional implicit surfaces; the student can change coefficients of the equation by changing a slider, and the surface changes real-time as the student moves his or her mouse. We use this in calc III.
TI-86 - Pretty nifty. My experience is old, I used to love my various TI calculators until I got Excel, and figured out how to use it. Not familiar with the current TI's, though it sounds pretty good, I seriously doubt a hand calculator can give quite the visualization and flexibility of a PC, spreadsheet, graphics and monitor. But, our schools must be practical too.
try a PC and the spreadsheet MS Excel for entering data and formulas, and use the graphics package in Excel for displaying the results.
You can do all kinds of neat things, easily and quickly, once you get the hang of it. And laying out and printing out the data in spreadsheet format and charts using Excel (while it takes a while to learn) can do/show most amazing things, in big screen and in multi-colors and 3-d.
Excel is highly programmable and full of hundreds and hundreds of built in functions - though they are not readily apparent. Get a good book on Excel and Customizing Excel will yield amazing results.
In fact, there used to be various TI emulators available, as add-ins.
To give you a simple idea in Excel - just enter in row(s)/column(s) of numbers and highlight them, and click on the little bar graph icon and create charts and graphs automatically. Enter formulas if you wish to automatically calculate the rows and columns of data.
As a mathematician, you should have a ball with Excel, after using the TI.