Wood floating shelves seem to have no supports lifting them. Actually, they are connected to the wall with a wooden strip (staple) that is screwed to the wall, and then the platform is connected to the wall by adjusting it on the wooden strip. These types of shelves can be bought new, but a cheaper (and more fun) alternative is to make your own from an old hollow interior door, and 2 x 4 wooden beams.
Mark horizontal lines on the wall with a pencil (use a spirit level) where you want to install your floating shelves. Using a beam detector, mark the location of each right foot along the horizontal lines. Cut the inner door along the desired width, using an electric saw (a shelf of DVDs can be 6 inches wide, a bookcase could be 8 inches wide). Measure the thickness between the two parts (veneers) of the door with a tape measure; Cut a 2-by-4 bolt with the same thickness. Also cut to the desired length of the platform.
Remove all corrugated cardboard interior from the door, on the side that attaches to the wall (cut 2 inches deep). The first and paint the shelves to your liking, using a brush. Nail each shelf for fastening systems using a Brad Nailer and 1-inch brad nails, starting at the center of each shelf and working towards each end (nail space 6 inches away). Wait for the glue to dry before placing items on the shelves.