pseudozach

This plugin disables the comment form until a user has sent a bitcoin micropayment over Lightning Network.

Pay to Comment with Lightning

Require the user to send a small payment before being able to comment on a wordpress blog.

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.

Pay to Comment with Lightning vs Flattr Comments