Simple setting image, you can also set position. This plugin unlocks unique image for each article.
This plugin allows you to add image for each artcile. You can set it easily in administration interface, because it has integrated button in media gallery for easier choosing image.
Image per article can make easy to remember article for visitors. They can imagine photo and associate it with your post.
That plugin also provide Facebook Share support (e.g. you have Share button and if you share article, the image will be showed as thumbnail in Facebook).