Ok, enough delaying, let's get this thing started! There are several ideas I have on magic, so I'll try to explain them as best as I can.
And by this I mean being able to throw around fire and lightening, teleportation, summoning and so on. This one has the obvious advantage of being the easiest to relate to, since it's a lot easier to point out at a guy who just roasted someone with a few words and say "Yeah, that guy's a wizard." then to point at the guy who seems to hang around historical landmarks a lot and doesn't really seem to do anything magical.
And of course, being this obvious also brings the main disadvantage of this - money. Doing special effects for the spells with a limited budget would be a bitch. It would either cost too much or result in shitty effects. Both cases are a no-no.
Of course, this could be bypassed by making spellslining like that rare. Instead, most magic would be shown trough rituals - magic circles, incantations, spells, incense - the works. These things will be able to accomplish a lot more complex things and cut down on the SFX too.
To be honest, I personally prefer this to the next one, mostly due to it's familiarity, as noted before.
The other thing that could be used is go for the Unknown Armies approach - strange and unusual magic, stemming from obsessions and weird logic. People buying themselves luck by taking risks, changing reality by getting drunk and being able to twist the memories of people by being history nerds.
This one is more or less the opposite of the "classical" magic I described above. The main advantage is the fact that most of this stuff is subtle and requires very little in the way of special effects. Making something fly across the room here and there, some filters and stuff - nothing fancy.
Of course, with being so weird also comes the main problem - it will be very hard for people to really get what's going on without needing tons of exposition on the matter, and I don't want exposition in the show unless it's vitally needed. (After all, the characters are supposed to already know this stuff and hang around other people who know this stuff. Why feel the need to explain anything to anyone?)
I guess a mixture by the two would be optimal. A wizard performing a complex ritual with candles, rare gems and tons of sigils and magic circles in order to enchant a cell phone or his laptop.
This one I like and would love to have in there. While adepts in UA just didn't really click with me as much as I would have liked, Avatars were something that really got me hyped up. (I've explained what an avatar is already. Go do some back reading)
It has both the advantages of the previous two - it's both fairly easy to explain and at the same time would, for the most part, require very little in the way of editing and effects.
There is something I just can't decide on, however. Ok, so characters could be able to draw their magic and energy from somewhere and something else, but the question is simple - from where? Now, this could be made just the way Avatars work - if you behave in a curtain way and surround yourself with the proper symbols you will be able to draw power from something bigger than you.
However, I also like what they do in the Dresden Files (especially the RPG) with the whole Emissary of Power thing. Basically, a character gets powers and magic from someone else - a demon, a powerful fairy, some god or something like this. In return, however, you have to do stuff for your sponsor.
And for the life of me, I just can't decide which one I want to use. In general, I would like if there weren't any obviously supernatural beings. A middle path might, again, be the best solution - You can gain power from a deity (this way I can get to use all these cool pantheons we have invented during our time on this earth), but will still have to cover themselves with the proper symbols in order to connect to it.
Now, I am imagining this as going along with either of the previous two possibilities, but I imagine it would be an interesting twist if humans are unable to draw power from themselves and have to rely on external sources to get their mojo.
Aaand yeah, this is all I have for now on the topic.