Hide information behind pictures, or behind white pen marks - when you rub it off it is clearly magic.
More ideas at: Are Interactive Whiteboards (IWBs) a waste of money?
Damn - I thought I'd invented something new but it appears to be a copy of this..
Copy, from google images, a picture which has something to do with your topic. (i.e. a picture of Ann of Cleves if you are studing Tudors with Year 8). On the floating tools bar select the pen and change it so it is white and as large as possible. Then white out the picture so the whole page looks white.
When the class come in all they see is a white, whiteboard. As a starter ask them easy/difficult questions about what you have been doing for the past few weeks. (This can get depressing as you realise they haven't been paying attention!). The student who gets a question right comes up to the board and, with the board rubber, can make ONE CONTINUOUS STRAIGHT swipe across the board. If someone gets the question wrong you hit the back button so the last swipe is lost. Students have to guess what the picture is of before the time is up/ 10 questions have been asked.
Easy to set up, great starter ad a lot of fun.