One easy way is to use Amazon ads as filler content. Rather than leave a right panel empty why not add an appropriate book or other product. If people are interested in the content of that page they are also likely to be interested in a book if it is closely aligned with the content.
Another way is to use books as news items. Depending on what kind of site you are running it can be difficult to come up with ideas for fresh news content and books can fill that gap. It takes only a few minutes to add a book of the month to your home page or carry reviews on the latest new release in your particular niche.
If you really want to go to town you can create a whole section of your site devoted to nothing but books. Use the Amazon tools in XSitePro to create content for appropriate titles and then add your own comments and reviews to that provided by Amazon to make the page content unique. If you really want to succeed this last step is important for two reasons. First, it adds value for your visitors, which is crucial if you want your site to succeed to its full potential. Secondly, it creates uniqueness, which means your page won’t get penalized for having exactly the same content as hundreds, even thousands, of other pages on the Internet.