Popular woods for framed garden beds include untreated pine, redwood, and cedar boards. Wood options will vary depending on your region.  If you wish to use a treated wood of some kind, be sure to do your research and determine whether it’s safe for your food. Note that the EPA banned lumber treated with chromated copper arsenate (CCA) for residential use in 2003.  Some manufacturers may claim their treated lumber is food-safe, but you must decide for yourself if you feel comfortable using it for your garden bed.