HTMLfixIT.com PayPal Instant Payment Notification script.
The HTMLfixIT IPN script is designed to work with PayPals IPN interface. It performs many security checks, logs all transaction data. With this script, you can sell items via PayPal and the IPN script will send out thankyou/receipt emails, keep track of pending payments, send you notifications of a transaction, stores a list of unique email address (so you can email clients easily if needed.). As an added benefit, there is sample code in the script that shows you how to set the script up to respond differently for different products you sell. (we use the script to automatically deliver the appropraite files when someone buys one of our scripts). For a full feature list, see <a href='http://htmlfixit.com/paypal_ipn_script.php'>IPN</a>.