Laserbits is another great place to find materials to laser etch and cut. They have many different products on their website including; acrylics, woods, stone, leather, rubber and chemicals for mark making on metal.
Some of the products they sell that may not be common elsewhere include their laser etchable rubber and other stamp making products, which can be found here. They also sell a variety ofCerMark products that allow you to leave marks on metal and ceramics. In addition to these more do it yourself from scratch products laserbits also sells prefabricated items such as clocks, key chains and plaques.
These are just a few things of note, it is encouraged for anyone interested in the laser cutter to check out their website, not only for their raw materials, but also for their technical tips and application information.