If you are an internet marketing or you build some blog or website for affiliate you may need to take decision to using this plugin for free. Ad Injection is a injects any kind of advert or other content e.g. Google AdSense, Amazon Associates, ClickBank, TradeDoubler, etc into the existing content of your WordPress posts and pages. And you can control the number of adverts based on the post length, and it can restrict who sees adverts by post age, visitor referrer and IP address.
You can configure any adverts in every your post as you want to. You may put the adverts randomly or on the top or bottom positions of your post, or also you may put it in any widget and sidebar. You can define multiple adverts for the same ad space which are rotated according to the ratios you define. And The number of adverts can be set based on the length of the post.
Try this plugin first for free before you purchase any plugin or widget.