As far as metals go titanium is not a good conductor. If one is worried about the bike drawing lightning strikes stay away from aluminum. Go for one of Calfee's bamboo bikes. Anyway at the power levels involved the metal involved is the least of your worries. Much more seriously laying flat on the ground is a good way to get fried. The ground current from all the electrical charges rushing to/from the strike will go through your body possibly killing you. The recommendation I've seen is to squat down with only your shoes on the ground and hold your ankles.