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.

zhenech

With Sexy RSS Footer you can add everything you want to the end of every feed entry. 
Backlink to the site? Sure. 
Number of comments? Sure. 
Flattr link? Sure. 
Something totaly different? Yepp, even that!
Suggestions for more replacement variables highly welcome!

Sexy RSS Footer

Sexy RSS Footer enables you to add any possible content at the end of every feed entry. This includes variables like number of comments, author etc.

Flattr Comments vs Sexy RSS Footer