I know Khan Academy has been mentioned by some 4/5 teachers in the past. Since Khan Academy is webbased it can be accessed on desktops, projector, and the netbooks. In addition, you should be able to access much of the content from an I-Pad, I-Phone, or Android.
For those not in the know Khan Academy uses video (YouTube) and the ability to try it yourself on the web site to teach math from the simple to the complex. Here is one on fractals that they are currently highlighting.
But that is not what I found so cool. Using your district gmail account you and your students can log on to Khan Academy. You can begin the process by clicking the Coach link. After students have their accounts they can add you as a Coach. This will allow students to navigate with their Knowledge Map as well as track their progress in their profile. As a coach you will be able to track all your students with a class report.
How much does this cost. Its free as in money and freedom. Khan Academy has a Creative Commons non-commercial share alike license which means you can do as you like with the content as long as you don't profit from it.
If you are using this resource I would be curious in how you are using it. Do you use it to model for the whole class with the projector? Do you use the document camera with a particular lesson? Have any of your students interacted on Khan Academy?