I came across The Writing Book by Sheena Cameron and Louise Dempsey, via a blog post from Juliet Revell.
I have been to a course with Sheena on reading a while back and found it to be immensely useful. I think I will have to see if I can track down a copy.
They have a Facebook page as well which I have 'liked'.
I have stored these writing ideas as prompts for later on when the boys get stuck.