Hi Peter,
I'm going to have a play with the Personal Recommends mod by Websitecm:
http://www.websitecm.com/x-cart-mods/x-cart-personal-recommends.html
See if I can display it at the bottom of the checkout/cart.
It has the options of recommending products based on cart contents or, if the cart is empty it will recommend other products - I think.
The ideal solution would be, to have thumbnails of recommended products at the bottom - but thats someway off yet.
Hebs