NASA's Jet Propulsion Laboratory has galleries of images of all sorts of things, most of them scientific. Many of these are impressive in their own right, but JPL also has an art collective known as The Studio - and they have crafted their own gallery as well. "Visions of the Future" presents sci-fi imaginings of a retro-futuristic travel agency marketing trips to planets within and beyond our solar system. Best of all, they (like all JPL imagery) are free to use within their rather broad Image Use Policy - basically the only things you can't do with the images on the site are sell NASA-logo merchandise or claim that NASA/CalTech/JPL as an organization approves of whatever you're doing with them.