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.

VoxPelli

Flattr was founded to help people share money, not only content. Before Flattr, the only reasonable way to donate has been to use Paypal or other systems to send money to people. The threshold for this is quite high. People would just ignore sending donations if it wasn’t for a really important cause. Sending just a small sum has always been a pain in the ass. Who would ever even login to a payment system just to donate €0.01? And €10 was just too high for just one blog entry we liked…
Flattr solves this issue. When you’re registered to flattr, you pay a small monthly fee. You set the amount yourself. In the end of the month, that fee is divided between all the things you flattered. You’re always logged in to the account. That means that giving someone some flattr-love is just a button away. And you should! Clicking one more button doesn’t add to your fee. It just divides the fee between more people! Flattr tries to encourage people to share. Not only pieces of content, but also some money to support the people who created them. With love!
Flattr requires an account at flattr.com!

Flattr

This plugin allows you to easily add a Flattr donation buttons to your blog and blog posts.

Flattr Comments vs Flattr