This plugin is including the Flattr button in your RSS/Atom feed. There are some more options to extend Flattr functionality like optional autosubmit
Easily add custom Flattr widgets to your posts and pages using shortcodes!
This plugin provides flattr-buttons for comments on your blog if the comment author entered a Flattr-ID.
This plugin is including the Flattr button for your blog inside a widget.
FlattrButton standalone lets you implement a Flattr button alongside a post, page or as a sidebar widget.