I use steel cored plastic levers a long the lines of the Park Tool TL-6.2. Mine are an off brand with the conventional spoke hook on one end. They sure help when the tire and rim combo is a tight fit, but still won't damage the rim. I keep a set in the shop and on the bike.
I also have a set of longer steel levers in the shop for when the youth group I volunteer for has a tire that just won't come off.