Sona can do great damage if you build her right. She also heals stuff, makes things run faster, makes allies do more damage, and makes her enemies dance.
Janna is awesome for disengaging team fights. She also applies a shield that can work on turrents.
Annie has a stun every 4 spells, and you could either to it to a single target or to a whole team. Also, her bear is a great meatshield for those pesky Blitz Grabs and Thresh Hooks.
Soraka has heals. A lot of heals. Seriously, a good Soraka will never let the ADC die.
Leona is the CC Queen. She can stunlock someone for a very long time. Great for zoning.
I personally like Braum. One, for his skill set. With his shield and his jump, you will save everyone. His passive is great for unexpected CC, and his ult can split the enemy team in half. Two, his personality is the best. After every game, all you want to do is to go out in a cold winter day with a pint of mead and sing happy songs. Three, his moustache.
Alistar is good, if you can get his combo right. If you can't, you'll just be ending up knocking the target enemy to safety.
Thresh is just overloaded. He has his hook that can either stop someone in place or set up for his Ult. He also has his Lifesaving Lantern. Then, he still has his Flay skill with can either pull someone in or push someone out.