Pure Titanium, (Water, Fire, Earth, Air) Titanium, Thunder Titanium, Dark Titanium, Sacred Titanium.
Pure could be used for "regular" skills (ie: Mystic Slash).
Elemental ones and Dark for Element/Darkness related Skills.
Sacred, being the less common one, for ultimate skills (perhaps even "summons").
For healing skills, Air and Water could provide them so we won't need a "Healing Titanium".
I like the Magic Levels and even more the possibility of combining Titanium in order to unlock hybrid skills.