Most of the types of magic I like are already in DF, but I figure I'd try to define the magical concepts I support - generally something a bit differentthan what people talk about here. The sort of magic that exists, for example, in LOTR. Magic thats... subtle. Old. Powerful, but enigmatic. There are no "spells". Err... I have a lot of trouble putting it into words.
Okay, how about this - magic isn't something you do, its something you make. You know that building things in a certain way will allow to to craft something that does something when around something else - the possibility of guided magic takes time, effort, but they have... durability. Magic, once created, lasts for a long time. In a way, it comes alive, because its not just something you make, its also the living resource that your crafting things from. And being magic, it sort of twists reality around it. Its effects take time, they are often subtle, but they are always powerful.
So in that vein, I think a few magical "concepts" are appropriate -
Animism - calling on the spirits of creatures rocks and concepts to aid or hinder. These spirits are fickle - they must be pleased. They will only help you if the proper traditions and offering occur, and if they feel like it. Dealing with them improperly can easily lead to their wrath. Included in this would be the concept of ancestor veneration and worship, with powerful spirits in life having subtle influences on descendents that show proper respect.
Wild Magic - Magical places and areas, especially old ones, where magic congregates, resulting in strange occurances. These forces are beyond the control of individuals, and will likely be covered by spheres, but I believe you should be able to have an impact - certain things you do should make it more attractive to certain types of wild magic. Places that have seen much in the way of death, for example, attract this. So that fortress thats fallen ten times and been reclaimed may start to see odd stuff as its spheres shift or multiple spheres start to overlap by being pulled towards it.
Magical creations - from the charms of the humans to the great works of the dwarves, this is like a scaled down version of wild magic. You build items and hope that magic is attracted to it. Doing it in a place strong with the same sort of Wild Magic is of course more likely to be effective. Forge your brace of necromancy in the volcano at the center of the lands of the undead, that youve primed by throwing a hundred prisoners into. As the death magic gathers around, you strike the final blow and the bracelet is forged. The death magic swirls around it, imbuing it, and you seal it in. The item is complete, and you take it away - but you still don't know for sure what it does.
Does it slowly rot the user, eventually causing them to rise as undead?
Does it, instead, make corpses close to the item hear the calling of unlife and wake hungry, hostile even to the bearer?
Or perhaps it is just cursed, sure to doom whoever holds it, and every victim becomes bound to it, their spirit forever traveling with it, bound up with the death magic?
THAT is the sort of magic I'd like to see, though obviously it would be incredibly hard to do.