What a tiny thing – Tinypass for WordPress, but it seems working only for standard setups.
There are questions to this plugin yet to be answered.
UPD: Micropayment paywalls are not an option for me yet. I do not like one step in their workflow – user has to upload his money first and they do not give change.
/it seems TinyPass does not work for WP setups from directory other than root. Am I mistaken?/