Wizards are extremely squishy, so any Nightmare/Hell/Inferno build must include several defensive options so that you can actually do damage (nothing can be cast on the run, so there will be no kiting anything to death with simple slows). Here are the priorities I've been using with my group of 4 to get through Hell.
1) Anything that stops mobs from attacking you at all is good. Mirror Image is the absolute best tool for this, as it does not have to be cast anywhere in particular, and can confuse even the most insane champion packs for a while.
2) Kiting is possible to an extent, but it requires manipulation of terrain via Teleport. Specifically, the Reversal rune (allows teleportation back to original spot for 8 seconds after first cast) provides more mobility than any other spell you have.
Things get a bit less clear from here, but I would consider Teleport and Mirror Image to be core on any Hell/Inferno builds.
3) Mirror Image and Teleport will not keep mobs off of you forever, and won't save you from Mortars, Molten mobs, Teleport/Fire Chains, etc. The point is that getting hit is inevitable, so you need something to help you take a couple of hits. At first, the various Armor spells might seem godly, but all three of them have some serious flaws (Energy limits AP and doesn't even give much armor, Ice only affects direct melee strikes, and Lightning doesn't even protect you), and the Galvanizing Armor passive itself is highly worthless when you have 15k+ Health and it gives a measly 200 life/second. With the entire school that is supposed to fill this role being useless, the only other defensive option is Diamond Skin, which thankfully has a wide variety of runes for different situations/difficulties.
Passives: Illusionist is your best friend. In Nightmare and onwards, it will trigger from almost any melee attack in the game and most special attacks as well. With Galvanizing Wards out of the picture, the next best defense passive would have to be Evocation, allowing faster Teleports, Mirror Images, and Diamond Skins. Beyond that, I feel that Astral Presence is simply a must on any Wizard on any difficulty, simply because it increases the ratio of AP spells to Signature spells, which makes you more consistent in any prolonged fight.
I find that teleport, wave of force with stun, and diamond skin is a good defensive build. I went through all of normal only dying 4(?) times. The only time I died from something other than slacking was when I was trapped by mobs with all three on cool down.