The Goodwill store at 2115 North Scottsdale Road, Scottsdale generally has a great supply of discarded dishes in its housewares department. Scottsdale folk have great junk. The one at 330 East Brown Road, Mesa usually has a good inventory of reject dishes, too. Dishes are the cheapest source of tesserae, but cutting them up is tricky, and working with the patterns on china is harder than it looks.
D&D Tile Services, 4802 North Seventh Avenue, has a fab selection of four-inch-by-four-inch ceramic tile and grout in every color of the rainbow, as well as the city's best selection on handmade tiles in shapes like flowers, mermaids, and hula girls. It also sells its wares online at www.mosaicguys.com.
Get a Leponitt mosaic glass cutter at www.mosaicbasics.com. Don't waste money on a knockoff brand of wheeled glass cutter; Leponitt is the only one to buy.
You can take a mosaic class most months at Desert Botanical Garden, 1201 North Galvin Parkway, 480-481-8164, and Southwest Gardener, 2809 North 15th Street, 602-279-9510.