This post is brought to you from Melanie of Violet's Buds. Melanie has Bachelors of Science in Photography and provides product photography advice and services to entrepreneurs.
Poster Board is one of the easiest reflectors to find and to use. Using white poster board will bounce light evenly, and won't create unusual tints of color are on your product images.
Depending on the size of the product you are photographing, a dry erase board is another good option. The slick surface bounces light well but sometimes can create harsh reflections if used in direct sunlight, so they are best used bouncing light around your product, but not on it.
White canvas board can be found at many craft stores & dollar stores, and is another great choice. It comes in various sizes and the matte surface creates a soft reflection and is easy to prop in place. If you have several canvas boards, you can use them as your backdrop as well.
Silver car window shades can be found at most dollar stores or at automotive stores. The flexibility of the shade helps when positioning, and is large enough for many sizes of product. A silver or gold-tone shade is perfect for portraits or modeled product photos, but may alter the color of product photos.
A few other things you can experiment with: a white sheet, aluminum foil, or a large sheet of white paper. Each material reflects light differently, so having a few choices on hand is a great idea to play with so you have the right set up for any lighting situation!
Do you currently use a light reflector for your product images? If so, what is your set up like?