Lynne Lee makes a good point over at her blog on article writing and marketing. She talks about writing pillar articles as a way to get more traffic to your blog. You can also use those same type of articles as a basis for an ebook. This is especially true if you are writing a how-to or other educational type of article. I have heard Jeff Herring refer to these articles as flagship articles. No matter what you call them, they can be the mainstay of your writing.