People often ask me what is the best tool to start with if you are using little to no technology in your class. Even though it differ a little from subject to subject my answer is almost always a document camera (combined with a projector of course).
If you have never heard of a document camera, imagine a modern version of the old overhead projector mixed with a webcam. Except is doesn’t project transparencies, it projects whatever you put under the camera. So no more preparing transparencies, you just put the worksheet under the camera and it is on the screen.
Do you want to give them an exercise from a different textbook? Pop it under the screen, you don’t even have to copy it. It is an amazing tool when you do geometry, no time is wasted drawing diagrams on the board, but you are still able to annotate the diagram as you go on.
I have also used the document camera very successfully to involve the learners when we mark the homework. There is seldom enough time for them to come up to the board and write their answers, now they can bring their homework and share it with the class immediately. (It has also done wonders to ensure that their books looks neater.)
The document camera can also be used to project experiments in the science or biology classes, or a webcam for class Skype sessions. If you connect the camera via your computer, you can take screen shots and even make a video recording as you work.
But the simplest models does not even require a computer, you connect the camera directly to the projector and you are set to go. For this reason even the more computer-phobic teacher in the school feel comfortable to use it. They are a fairly expensive piece of equipment, but we have found that where we have bought it, it is being used optimally. (Not something you can say about all gadgets.)