I have a connected question, and you guys seem to be plenty smart on making builds.
I'm going for a wizard type, who focuses on magic and maybe other things. My main offense will be with destruction. So my build is full destruction, a few points into Alteration for the mage armor, and then some points into Restoration for some heals. It ends up with about 30ish points, what do you guys think I should put perk points into after that?
Since you are going pure mage, you must have ways to sidestep those situations that render your character useless: 1) when he gets silenced 2) when he runs out of magicka. In that sense, I propose alchemy to build a good stock of 1) dispell potions 2) magicka potions. That should be your top priority in my opinion. However, even if you go down the alchemy route it's not clear to me that restoration becomes redundant. Restoration is more than healing: it has a full set of defensive spells against warriors and mages that can be very useful. Also, its perk tree have perks that increase magicka regeneration.
Also, and as Archayon said, enchanting can be very useful as well but only if you invest heavily on it. Think about it this way: you don't want to run out of magicka so enchantments that accelerate your magicka regeneration rate and enchantments that increase your magicka pool are very useful. We know that mage robes and hoods do that, and the percentages are VERY nice (mage robes: regen 50% faster, necromancer robes, regen 75% faster, mage hood : 30 more magicka points...). So if you have already this kind of gear around, why enchanting? because of the double effect perk. Enchanting each item twice could turn you into a powerhouse, however, you will need to raise enchanting to level 90 to do that. Not sure if it's worth it...
Illusion on the other hand can be an interesting avenue with all this command and frenzy spells (useful when you are outnumbered). The downside is that if you use illusion more often than "when extremely necessary" then your other skills will not increase that much (in my opinon Illusion is versatile enough to be the main skill of a build).
So, what I would do:
Destruction
Alteration
Restoration
Alchemy
If you still have perk points to invest:
Enchanting (if enough to get the "extra effect" perk and at least 4 ranks of the "enchanter" perk)
Illusion (if you have some perks left but not many)