If you need to display a working scientific calculator to the whole class, look no further.

http://www.ecalc.com/calculator/scientific?ca=BCALC&typ=MIO&src=USB&vrs=...

You can also download a free virtual four-function calculator that can be carried with you, eg on a memory stick.

http://www.ecalc.com/files/mio/ecalc/basic/usb/calculator.exe

For ActivStudio software. Doo-dahs are a wonderful way to bring information into a classroom discussion in a controlled manner. A Doo-Dah can contain text, annotations or images, even those added or created on the fly. A picture is worth a thousand words, so download the file and have a play. You will soon learn the power of doodahs!

If you have group competitions in your class, this is a neat way to keep a running score (up to a maximum of 30 points per team).

A wonderful collection of clocks. The time comes from your computer's system clock, so if that is correct, these clocks are as well.

Click on Edit and paste in a list of student names or words.
Click on either 'Typewriter' or 'Fruit Machine' to have the program randomly select from the list. A neat bit of programming. With the Fruit Machine, you can remove the names once they are chosen.
http://www.classtools.net/main_area/fruit_machine.htm

A virtual geoboard. A very nice implementation.
http://standards.nctm.org/document/eexamples/chap4/4.2/index.htm#applet

The Magic Magnifying Glass can be used to reveal hidden words and pictures.

For those who don't have either Equation Editor or MathType at hand, here is a free on-line equation editor. I had a play with it, and it seems to be very good:
http://www.sitmo.com/latex/

You can create your own graph paper (Cartesian, Engineering, Polar, etc) right on this website. The output is a downloadable pdf file. Very handy.
http://www.printfreegraphpaper.com/

And here is another site that has free printable graph paper:
http://incompetech.com/graphpaper/