WordPress Printable Gift Certificates plugin provides a platform for service based businesses to sell and manage “printable” gift certificates that can be redeemed at the time a service is rendered. It allows you to create set Gift Certificate amounts to sell from your Blog or Website via PayPal. When payment is made through the PayPal Website notification is sent back to the plugin and a unique gift certificate is created and e-mailed to the payer. Each gift certificate includes a QR Code which can be scanned from your smart phone and will provide instant verification of the Gift Certificate and amount (requires access to the internet).
Plugin homepage: http://www.suburbanmedia.net/wordpress-plugins/wp-gift-cert