PALLETS
Pallets are probably the best resource I came across. They are free and provide endless possibilities. I used them to build my fence around my garden, as well as the planter boxes, benches, and decorative touches. Remember, you can break them down and use the individual pieces to make almost anything, so do not think you have to keep them in their original form.
When looking through the piles of pallets, keep an eye out for ones that may contain additives or chemicals that they use to treat the wood, these will be clearly marked. Use common sense when choosing them, the color, texture and even smell are all indicators of treated wood. You can ask someone for help if your still unsure, do a little research beforehand, it will make this part much easier. If you're going to disassemble the pallets and use the individual pieces of wood, try to do so without damaging the wood to badly. Pallets are held together with spiral nails which hold very well.
A few tips on dismantling outlets: -use a flat bar and pry the wood up gently to raise the nail head up, then knock the wood back down. The nail should be protruding out of the wood now and should easily pull out. -If you have a sawzall handy, you can simply cut the nails off. Then use a punch or nails set to pop the remaining nail and nail head out.
ROCKS
Another one of my favorites is rocks I find around my yard. These are also free and provide multiple uses like pallets. I stacked mine to make attractive planters that separated the different types of plants I planted. I use them for all of my herbs, this was a great way to easily identify my herbs and organize my garden. I also created a dry creek bed to add some style and appeal. Mortar can be used to create beautiful walls, borders, and pathways. That may require some masonry "know how" but is very simple to do if you do your homework.
BROKEN CONCRETE
I love broken concrete .... Most people see an expensive dump run when they look at chunks of concrete, I see about a million uses. I have used pieces to make stepping stones, faux rocks, a pond, artwork, the list goes on and on. You can find pieces in several places, construction sites, lumber yards, and even Craigslist are just a few examples where I have found mine. People are more than willing to let me haul it away.
You can make steppingstones very easily using pieces of broken concrete. Start by finding a good size piece of concrete, that is fairly flat in shape. Apply a coat of mortar over it to smooth the surface out a bit. Next, take a large paintbrush, or a mason's brush and gently pat the surface to create a textured surface. Cover the rock with a piece of plastic and allow it to cure overnight. When cured, add paint, or stain to create a contrast of colors. Imagine a real rock and it various colors and textures. Last, apply a sealer and allow adequate drying time.
RESOURCES
There are many places you can find free materials for all of your projects. Search around and ask others for ideas. Browse Craigslist, your local building supply stores, warehouses, even a job site, ask the person in charge if you can have the unwanted materials. Post a classified ad stating what you are looking for or where you might be able to find it. Use your imagination and think outside the box