Although this is a time consuming process at times, I'm planning on redoing the spell casting system for my game.
At the moment in order to cast spells you have to take an appropriate spell casting Talent, which opens up the appropriate skill. There are two talents at the moment and each opens up one of two skill associated with it.
The skills determine what spells you can actually cast.
The first talent is Thamaturgy, which lets you choose between the skills Enchanting, or Thamaturgy.
In essence these are Arcane casters.
Enchanters are the buffers, their spells have to be cast on someone or something.
Thamaturgy are a combination, their spells are more attack oriented, although they do have minor buffs and a very minor version of heal.
The other Talent is Faith, which lets you choose between the skills Channeling, and Devotion.
These are the Divine casters.
Channelers are similar to clerics, they have one attack spell to choose from, while the rest of their spells focus on healing damage, curing diseases, removing poison, and a few minor buff spells.
Devotion casters are interesting to me. They are the only caster type that has access to all of their spells. Whenever they cast a spell it is more along the lines of praying for an affect, but the affect that occurs may not be exactly what they want, it is up to the deity they worship as far as what spell takes affect. They do not have any attack spells, but the spells they do have access to are very powerful compared to the other casters.
Although I do like the way it is set up, the times I have gotten to play it has not been received quite so well. Not only that the different talents giving access to different spells in essence seems to create a magical class system in a game where there are technically no classes. Also with the more I think about it, the more I realize that not all, but most stories I read with spell casters, there are not usually distinctions between them, and someone who can call down fire and lightening can also potentially heal at least slightly. Although this is not always the case, I like the feel of that better for my game.
I am still working on the specifics, but what I would like to do is make one spell casting talent
that grants potential access to all the spells for players. As far as figuring out how to regulate how they are at actually casting a spell is part of what I am still working on.
Eventually I would like to work on a more free form spell casting ability, although I do know that the majority of the people I normally play with will never play a more free form spell caster.