In fact a skill and feat magical system that is based around a system of spheres.
say the standard Earth, Air, Fire and Water,.. also Life and Death, Light and Shadow, maybe Spirit or Mind.
Each of these spheres represents certain magical effect types i.e Air = movement, fire = damage, agression, water = health, and change etc..
All spells could then be made up by drawing upon those spheres..
A healing spell would be water and light a fireball Fire and Air, a polymorph spell water and life, an animate dead spell air and dark...etc..
Each spell could have a casting DC and the casters strength in the various spheres would provide a casting bonus to thier magecraft or spellweaving whatever you choose to call them checks.
I've always been quite taken by the idea of weaving threads of magical energy from different sources to make spells.. with a system like that you would have your basic spells but have in place asystem that was dynamic, if you wanted a fireball to do more damage you try to weave more fire to it, thereby increasing the casting DC, failure possibly weakening the mage or if fumbled resulting in some magical backlash as all the threads unravel unleashing the magical energy.
Also this way you could more easily have mages specialised in casting certain kinds of magic.
enchanters could be skilled in infusing items with threads and tying them off in order to give them lasting or temporary effects.
crerating golems or constructs, homonculi etc..would simply be a matter of weaving the threads to give artifical life and movement, and the like into the constructed bodies...and tying them off.
Your generalists would be okay at casting a variety of spells but to truly master a sphere a caster would have to specialise and thereby gain access to more powerful spells and effects in there sphere of specialty.
Magic should be taxing.. it should be fatiguing to cast and the more you draw on the spheres for a particular casting the more it should take out of you.. mages should be able to use minor effects often but more useful or potent effects only now and then without resting between in order to remove the fatigue.
Certain areas could be strong in certain spheres and make casting certain magics easier or more diffcult while in them.
I also kinda like the idea of civilisation and magic being alternate sides of a balance.. magic having less effect and being more difficult to use in areas that are more given over to science and civilisation.. magic should be as much about belief as it is skill.
As for DIVINE Magic, I've always wanted players to be required to act like the faithful in order to be granted thier divine powers, miracles should be eartn through service and devotion, pushing the belief and cause of thier gods, vanquishing thier enemies..it should be a proactive system based on rewarding good service.
Perhaps characters could have a Faith rating that provides a bonus to attempts to call on thier god for aid.. gods could provide certain benefits based on thier nature and the diffculty of calling on them could vary based on the characters prayer roll plus thier fath bonus and maybe also modified by the faith modifier of the region they are in..this way the more known and active thier god is in a region the more likely they faithful are to be heard and responded to. This creates a system where players can push thier faith at every turn, if you buiold a temple or convert a village it will increase your gods fiath rating in a region, which in turn makes him more likely to respond to your prayers for aid.
War gods could give combat bonuses to thier faithful, nature gods could bless crops, or promote births, provide healing, or summon animals etc..etc..
what do you think?