1) BACK END CATALOGINGSend your customers a catalog of add-on products for original product they purchased. This could be upgrades, special services, attachments, etc. If they enjoy your product they will buy extra add-ons.
You could charge other businesses for including their products in catalog too. This'll help to pay for postage, packaging and producing catalog. If you want to cut costs, produce catalog in email or ebook format.
2) GIFT CERTIFICATES
Sell gift certificates for your products. You'll make sales from purchase of gift certificate, when recipient cashes it in. If recipient never uses gift certificate, it adds up to a huge profit.
When people do use their gift certificates they may also buy other products you offer while they are shopping around your web site.