Wesley Tansey proposes a number of techniques for generating startup ideas. The techniques are useful tools to expand your repertoire of techniques, but the key point, in my opinion, is after the list:
One important thing to remember is that these are not meant to be options that you choose at the start. Rather, consider each of these strategies to be a background process that runs continuously in your mind. Every time you encounter a problem, if it may be solvable by one of these strategies, that's a potential startup idea!
This echoes what I've pointed out before: the way to generate ideas for businesses begins with a continuous process of evaluating business opportunities, rather than business ideas, around you.
That said, once an opportunity has been flagged, Wesley's techniques can help to define what sort of opportunity it is.