I confess that I am a bit cranky when it comes to WordPress plugins. I use as few as possible (to not compromise my WP install), and I also tend to like some old school plugins that were released years ago. My plugin of choice for adding a link to my RSS feed, for instance, was the sig2feed one. I started using it early in 2006!
Recently, however, more people started scraping Daily Blog Tips, so I felt that it was necessary to add not only a link back to the blog, but also a link back to the original post. This should help Google to identify my original articles more easily and quickly.
When I tried to use sig2feed for this purpose, however, I found that it was not capable of (not without a good deal of PHP tweaking at least), so I decided to find a new RSS feed footer.
RSS Footer is the name of the plugin created by Joost de Valk, and it gets the job done perfectly. Basically it allows you to insert any message or link on the footer of your feeds, and it also comes with a check box that you simply need to tick if you want a link back to the original article.
If you have people scraping your RSS feed, give this plugin a try.