I recently spent a couple of weeks intensively working on my sight-reading. I started along the lines suggested by Simon - I played through all the pieces in the Delcamp collection from level 5 to level 8. Then I sorted my collection of music, and in doing so played them all. I played them straight off, no more than a few moments preparation, and no repeating. Of course there were some that I could not handle, but many that I could make a passable attempt at. I have gone through as many texts and samples as I could find. Recently I stumbled across this thread
in which there is mention of the AMEB sight-reading text, so I have ordered a copy of that in the hope that there are some useful pieces in it.