You can make raised beds from such common materials as concrete blocks, bricks, railroad ties, pressure treated lumber, etc. Railroad ties need to be completely dry before using, as leaking creosote can affect your plants. Pressure-treated lumber may be unsafe for use in the garden if treated with such chemicals as pentachlorophenol. Be safe and aware of the hazards of using treated wood in the garden.
Kits are available so that you can easily build your own raised bed from beautiful hardwoods like cedar. You can also buy kits that are made from polyethylene blocks that look like natural stone and work pretty well.
You can find a complete selection of raised bed gardening kits at Clean Air Gardening.