I'm with Denver and everyone else on the wiggle technique; start at the valve and get both beads into the bottom of the channel and grab the tire carcass with both hands and work away from the valve, creating as much slack as you can when you finally get to the side opposite the valve. Done right, you might have enough slack to push a bead over the edge of the rim w/o tools. Otherwise, I'm fond of the Michelin tire levers below; they're not conducive to hooking onto any spokes, but they're nice because they're very flat, very skinny, and much tougher than they look.