Download Here: http://drupal.org/project/lm_paypal
Summary
This module provides an interface to PayPal using Instant Payment Notifications (IPN). It currently supports paid memberships (subscriptions), donations (tip jar) and paid adverts (classified ads).
Thoughts
I used this module to help stage a site for someone that required a "paid subscription content" site. He wants to have content that only his paying customers have access to. There were several modules, but the lm_paypal seemed to be a more robust / configurable module. lm_paypal supported auto renewals, different subscription term periods (days, weeks, months), as well as multiple subscriptions.
One thing to note is that you still require a "node access control" mechanism. lm_paypal provides a mechanism for people who pay to be assigned to a "role". It is then up to you to use your node access system to give that role (and that role only) access to the paid content. I chose tac_lite as a simple module to get the job done for my needs.
The logic I used in creating the paid content was to create a "Subscription01" subscription, a "Subscribers01" role, and a "Subscriptions" taxonomy with a "SubscriptionContent01" taxonomy term. Using tac_lite you can grant access to the SubscriptionContent01 tagged content to the Subscribers01 role.
lm_paypal also supports paid advertisements and donations, but note this is NOT an ecommerce module. There are much better modules to meet that need.
This demo site is still a work in progress and I will be sure to update this page with any other tips/tricks I run across.