Texas Instruments also manufacture a product that allows you to view the screen contents of a calculator with supported hardware on a TV;
I do not have one of these calculators, just a plain old TI-83+. However, this calculator (as well as the older TI-83 and TI-82) allows you to capture a screenshot over the link port. Pressing a button on my device captures a screenshot in this manner and displays it on the TV. This relies on the calculator being in a state where it can respond to these screenshot requests, so is not ideal, but considering that the TI Presenter costs $300 and relies on special hardware inside the calculator and mine should cost less than a tenth of that in parts and work with older calculators I think it's a decent compromise.
Click for a gratuitous 360? view
I had previously believed that NTSC composite video signals used a negative voltage for sync pulses. I have since found documents that indicate that the sync, black and white levels are the same as those for PAL. The timing is, naturally, different but as there's no need to change the hardware it makes supporting both NTSC and PAL relatively straightforwards. This contraption can be set to operate in either NTSC or PAL mode by sending the real variable M to it from the calculator, with a value of 60 for NTSC and 50 for PAL.
I acknowledge that this is not the most useful of projects (unless you're a maths teacher with an interest in electronics) but the code may be of interest for other projects. A handful of inexpensive parts can get you a picture on a TV from a 96x64 monochromatic frame buffer (the 1KB RAM on the ATmega168 doesn't allow for much more, alas).
More information and downloads can be found on the TV Demonstrator project page.