So, inspired by the TC's idea for a magic system, I decided to come up with my own system. I came up with this one to specifically be as flexible as possible, yet still maintain a magical feel.
The primary source of magic is life, so any living creature will provide a little bit of magic, some more than others. Plants have a special magic as well, with trees having much larger amounts per specie than lesser plants (which provides an explanation as to why the Elves get so pissed off when you cut down too many; it kills off some of the magic as well). Humanoids are stronger sources of magic than most other creatures (one exception being (semi) Mega Beasts). So, a large civilization will have a constant flow of strong magic flowing out of it (to where, I'll get to in a minute). Because of this strong source of magic, it would possibly attract wizards (lots of magic = more powerful spells for the wizard), necromancers, Megabeasts, spirits, zombies/skeletons (perhaps only if in the vicinity of an evil area), etc. etc. Having the wizard be a noble would be interesting, and the noble could teach magic to promising children. Gods and Spirits let out huge amounts of magic (Which is why Elves would worship Spirits, they are sources of magic as well).
Not all dwarfs produce the same amount of magic, but its not entirely random either, just a normal distribution. Perhaps only dwarves that are ~2 SD above the mean have potential for magic, and not all of those would even want to learn. Anyways, because its a normal distribution, the game wouldn't need to calculate the magic for every dwarf in world generation, it would just need to take an average of the population.
I like the magic flows idea presented in the previous topic, but some stated it best when they said "Great. More flows." So, instead of a flow, I think there should be streaks of magic flowing across the world, at very stable levels. The streaks wouldn't be visible, but they would be fairly predictable. Magic would starts at densely populated areas, and try and flow towards the north and south of the map, but would get diverted by the evil and good areas. Evil and good areas both are magical in nature, but they use the magic differently.
Good areas gather magic, but they compound it, slowly increasing how much magic is in the area. Thats why plants grow quickly, and there are special plants there; a special magic is in the air, making things more lively and joyous. Also, part of how it increases the magic is by increasing the amount of plants in the area.
Evil areas, however, consume magic, and will strip it for its malign purposes. I propose that this is one way that skeletons are created; skeletons are animals that lived for too long in an evil area, and had their natural magic consumed. They are so aggresive because they want their natural magic back, and attack anything that has this natural magic, like everyone's favorite race, the dwarves. However, the major civilizations are much more resilient to said magic, as their natural magic is more plentiful.
If anyone has read the Belgariad, they will know what I'm going for in the magic system. In order to do something magically, one has to thoroughly know (either intrinsically or through study) what they are trying to accomplish. If you point at a rock and tell it to become a bird, if you don't know what a bird looks like, what its general bone structure is, etc. etc., then it will be nearly impossible to do. So, magic is more about knowledge and less about magical incantations and more about knowledge. No Harry Potter magic here.
So, to put it all into place, places like old forests and jungles would have fair amounts of magic, deserts and mountain tops wouldn't have much magic (unless a stream is passing over it), and civilizations would have the most, with Elves producing the most, then dwarves, then goblins, the humans, then kobolds. Some humanoids have enough intrinsic magic to manipulate it, almost all greater beings are guaranteed to be able to. There would be more elven wizards than human wizards, because Elves are more intrinsically magical. Good areas would have lots of magic to play around with, evil areas less, because you have to compete with the "source of the evil" for magic. The areas between the streams would have quite a bit of magic to play around with. As an outpost grows, the fact that its more magical would draw the attention of various megabeasts and other civilizations.