My favorite places to find landscaping materials are through my local Freecycle group and Craigslist. People are constantly tossing out pavers, wood and planters and you can pick these up for free. We built six raised beds out of old cedar decking we received for free if we would just haul it all away. We also built a raised terrace by our driveway from discarded patio pavers. The extra pavers were used to create a border for our fruit trees and a retaining wall around a pond.
For the pond, we got real creative. A scavenged storage tub holds the water. Decorative rocks fill in around the tub and disguise its edges. We made our own biofilter from an old decorative terracotta pot, sponges and a purchased pump. The entire pond cost us only the $15 we paid for the pump.
Plants are given away freely in spring when people are tearing out old plants or dividing their perennials. Nurseries will sometimes give away weak or wilted plants, which if you have a green thumb and can nurse them back to health is a wonderful deal. Plain nursery pots are also usually given away by the truckload at any store that sells plants.
A variety of found objects can decorate your yard. Old metal wagons can hold flower pots. You can fashion old clay pots into bird baths or turn an old but attractive sink into a planter or bath. Look through garden sites and magazines for inspiration, then scavenge in your town for materials to bring the dream alive.