I'm constantly adding new designs to my Cafepress, Zazzle, Spreadshirt, Mysoti (well, not so much these days), and Prinfection stores. If you're not familiar with these sites, they're all print on demand companies. I create designs for t-shirts and other products, upload them, place them on the appropriate items, and offer them for sale. Products are produced and shipped by the company. There is no inventory, but since they're usually made one or two at a time they tend to be more expensive than similar mass produced items. I retain the rights to my designs and can use them in as many stores as I like. This is good, since they all tend to have slightly different selections of items to work with and price ranges.
Most of these designs are printed on shirts or other clothing but there are other items available and I've tried to mark the ones that are only available on non clothing items. Links to Cafepress or Printfection often lead to pages with multiple products for sale but Zazzle doesn't have that option. If I have multiple produts (including designs specificaly for light or dark clothing) for sale there I'll include links to all of them. Links to Spreadshirt take you to the product designer where you can select whatever product you want to print the design on yourself. You can even search for and add other designs or text for complete customization. Designs labled as "Vector" have been simplified to a maximum of three solid colors and the product designer will allow you to pick and choose each of those colors yourself.
I also have items available on Shapeways that are not simply printed onto other products but created from scratch with 3D printing and come in a variety of materials like plastics, steel, silver, and ceramics. Prices vary between the materials you order it in. The materials each model is available in depends on the size and geometry of the item.