A powerpoint of words which are commonly spelt incorrectly. Simply open the presentation on your IWB, set it to full screen and read together as a class.
I have all children seated on the floor with a whiteboard and marker. After we have read some words together, I will ask them to write down the word which was previously on the screen.
I.e. they > then > this, ask children to write 'then'. Check once they have all written the word. I ask my class to hold it up when they are done, then go back a slide to show the spelling. Rub it out with a tissue or their finger and repeat!
Note - You can add as many more words to this slide as you like, or even remove some current words if you don't want them.