I used to have a book from a game called Bloodshadows, it had an interesting method in it's magic system. Every spell had a skill component and a power component. The skills were similar to evocation, abjuration, alteration, and conjuration, etc. The powers were along the lines of pyromancy (fire), geomancy (earth), aquamancy, necromancy, vitomancy (life), and so on. Creating a golem under this system was a conjuration:vitomancy spell because you were creating the life force that animated it. The default fireball was evocation:pyromancy but there was a half page "sidebar" called 'Focus on Fireball' that detailed something like six other ways to make fireball spells. These included versions like an alteration:chronomancy that brought ashes back to fire, a conjuration:photomancy that used light, and a something:necromancy that used trapped 'corpse fire' (a magical St. John's lightning-like effect from graveyards) to make the fire.