I really like Thresh, Taric and Alistar as supports as of posting this!

Team Protection: Thresh: Has The Lantern which is both a shield and repositioning tool; also has The Box and The Pushback Whip Attack Thing to help peel for his teammates. Taric: Has a point-and-click stun whose cooldown can be fairly low, and a passive armor buff and a heal which synergize flawlessly - something something gems. Alistar: MOOOOves people out of the way of his teammates with a knockback and a knockup, and has a neat aoe heal move.

Damage: Thresh: The Box hits like The Truck now which is The Awesome. Gets a lot of damage on his whip attacks too. Taric: gets a BIG flat AD bonus from ulting AND has armor reduction, and also has a lot of magic damage on his E against up-close targets. Alistar: Nothing he has does a lot of damage in particular, but everything he has does pretty good damage. All Three Of Them: Have bits of magic damage strewn about their kits which is rewarding to make good use of where possible.

Initiation: Thresh: The Hook, The Pull Himself To People and The Box make it extra scary to mess with him while his teammates are around, especially for lower leveled champions. (if nothing else, this in particular makes him perfect for botlane btw) Taric: Has no incredible initiation in particular, but everything in his kit generally encourages teammates to stick close to him and go HAM. Alistar: has the sacred combo he's had since season 1 and an ulti that essentially says "Don't worry team, I can tank anything. Ban Vayne".

Warding: Thresh: Slaps people a way with The [insert overused jokes here], making it hard to catch him. He can also pull himself to any hostile units. Taric: Is so tanky that he is essentially a ward on legs, except instead of being invisible no one wants to bother to try to whittle him down. Alistar: see Taric.

I can clearly see reasons I would want to pick any of these champions as a support. The only qualm I have is that Riot hasn't made 10 more champions like them! In terms of gameplay at least. From my perspective I don't see many good ranged supports aside from Thresh (who doesn't have a lot of range to begin with) that are valuable as a support; they're too "hands-off" to help teammates as much as they could. They're very self-centered, generally speaking, despite Riot having given them so many good supportive moves; it makes it hard to appreciate playing as or against them.

Riot should come up with formulas for ranged supports that are as rewarding to play as these supports!