The Upsell Offer module is perfect to maximize sales volume by increasing average order size using up-selling technique.

DOCUMENTATION
http://www.oc-extensions.com/Upsell-Offer (see tab Help)

DEMO
Store: http://demo5.oc-extensions.com/modules/

Admin: http://demo5.oc-extensions.com/modules/admin (user: demo pass: demo)
Click on Checkout link to see the first upsell offer. After that add Ipod Nano to cart and click again checkout to see the second upsell offer.

CHANGE LOG
http://www.oc-extensions.com/Upsell-Offer (see tab Change Log)