Strong Supports So Far
I am not going to mention Soraka, because Soraka is straight up broken and needs a rework, but mage supports are definitely one of the top tier supports I say; but remember most of these champions have high skill floors and even higher skill ceilings so they are not simply "pick and play" champions. Remember Soraka is a brain dead champion and requires no skill to play.
Strong supports right now (all being done with combinations of 0/18/12 masteries): Nami and Zyra are back baby! Nami benefits highly with 0/18/12 having the heal buffing mastery and keystone, as well as the summoner spell cooldown and the obvious in Cunning. The thing to why Nami is strong is because she has always been a gold reliant support, but if you maximum the gold on the spell thief (and the mana regen she needs) at its tier 2 and more mana regen on tier 3, the gold is 17 gold per 10 which is a lot of gold as long as you are not sitting on 3 stacks then you have perfect uptime of gold regeneration.
Zyra on the other hand is a lot less gold reliant than Nami, but she does benefit highly from the spell thief line, especially the increased damage and the fact that she procs the stacks so easily with her plants, abilities, and basic attacks (this helps her get bandit gold too); but Zyra also proc and benefits highly from the flat magic pen for her base damages and Thunderlord's Decree. She also benefits from corrupting potion both with the damage and the much needed sustain. Zyra does a butt ton of damage and you should have one of the highest, if not the highest in some games, damage dealt to champions... AND YOU ARE THE SUPPORT REMEMBER!
Others that are strong are general mage supports: Anivia is strong under the same set up as Zyra, she is more gold reliant like Nami obviously, but she basically does everything as well as Zyra in terms of proc the spellthief damage/gold and thunderlord's decree, 600 units basic attacks proc bandit easily, and all the mana regen on the sightstone enchantment is what Anivia needs the most, your next item you probably want Athene's Unholy Grail into Liandry's Torment if you get to that point; and cooldown boots is the best for summoner spell cooldown and cheapest option.
Vel'Koz is basically under the same context of Zyra in all aspects, but less damage, and less reliable damage besides for his ultimate (its pretty hard to mess up a Vel'Koz ultimate).
Veigar and Annie are in the same category, where they are bursty with lower damage aspects than the others, but they have game changing stuns on their basic kits; in short, they are stun parts,
Kennen will be pretty decent as well; but he is better as a solo laner, or better yet marksman Kennen with Gunblade into attack speed items like Hurricane, Shiv, etc. Kennen will be under the same premise as Annie and Veigar and be stun bots.
Brand can work as well, but the others are better than him; his damage output is very high however.