Michael Henke

This plugin provides flattr-buttons for comments on your blog if the comment author entered his Flattr-ID. 
There will be an additional input field right below the comment text box. Alternativly you can input a piece of code in your theme to place the field somewhere more nicely.

Flattr Comments

This plugin provides flattr-buttons for comments on your blog if the comment author entered a Flattr-ID.

This plugin will create a Flattr button in you RSS feeds item. Feed readers whith support can then show the button below the text, so that readers can Flattr directly from their RSS reader.
Flatt RSS plugin requires an account at flattr.com!

Flattr RSS

This plugin is including the Flattr button in your RSS/Atom feed.
There are some more options to extend Flattr functionality like optional autosubmit  …

Flattr Comments vs Flattr RSS