When I usually draft I like to keep in mind the heroes who are LONG forgotten, but still way to good to pass up when none of the dendei heroes fit your team.
Ancient Apparition: He offers your team a lot of versatility, while being able to mid or support he can be picked up as a fifth pick (also good counter to slark and alchemist). He combines well with a carry+a support with a disable. He offers great teamfight as well.
Disruptor: This hero offers a lot of teamfight and gank, while lackingBURST. His ult and field can just wipe teams, while glimpse can be a really hard to deal with spell. He is a good combo with aa and Jakiro who are on this list as well.
Jakiro: This hero used to be the go to support, but I still think he is amazing. His stun is hard to compare to anything else, because it's so GOOD. He can offer very high teamfight and great aggressive lanes. He is also really tanky (something a lot of supports aren't).
Lion: This hero is currently really underrated, but my friends love him, so I draft him. He has a LOT of disable, while also being able to BURST somebody down really quick. The way we like playing him is getting him his level 6 secured than looking for 100% kills.
Omniknight: The way we just ran this hero is solo safe lane while we had an agressive tri, and boy is it GOOD! He has to farm his quick arcane, mek and vlad's and you WILL win fights. His heal is super strong and his magic immunity is WAY undervalued.
Ogre Magi: He is my personal support, who while being melee has a lot of damage, and steroids in the late-game. While being tanky trough the entire game. His roams are really deadly even at level 1 or 2.
Witch Doctor: He IS the most underrated support of all, while being squishy he has the best stun in the game, a great heal, a HUGE damage amplify and a team-wiping ult. I personally don't get why people don't use him.
Share your experiences with these heroes in cm.
Cold Feet might be 300 damage and 3.5 seconds of stun...or 50 odd damage and no stun at all. (I agree btw that Chilling Touch is underrated, that's 450 damage for a trilane at level 1).
Witch Doctor can work wonders with the right combinations (him and Warlock is pretty awesome, but that's a weird, weird lane to setup), and much more farm than a standard support is likely to get. Do the team really want their 4 rushing a Mekansm or a Black King Bar? Not a tough one, that. He's awesome combined with Medusa and Faceless Void...but how often do you see them in a competitive game?
Basically both of them are generally consider "too inconsistent" for high level play, as although their high points are better than their rivals, their low points are much lower too. Generally people want supports to be as reliable as possible.
Still, since WD is a really bad roamer and ganker, I don't see him as a viable pick; his lack of survivability and his (very easy to stop) ultimate that makes you vulnerable are also a disadvantage.
Nothing to say about Disruptor, Jakiro, Lion and Ogre Magi, I like all of them. On the other side, Omniknight is a bad core Hero but still needs some farm in order to be effective; I can see him as a viable off-laner if you need a fast Mekansm, but he doesn't deal much damage in teamfights and ganks (though his utility makes up for it).
And lastly, about Ancient Apparition: I think he's a really situational and lane-dependent Hero. If you don't have a global team, even if you want to counter a Slark or Alchemist there are better picks ( Bane on top of the list); on the contrary, if your team consists of Zeus, Faceless Void, Nature's Prophet or Spirit Breaker the ultimate helps a lot. And about being lane-dependent, I think pairing him with a Chaos Knight or any other stunner is a must-do unless you want to play very passively.
Another thing I noticed is that everyone underestimates Chilling Touch: it's actually a fantastic ability (the most useful on AA for me), the damage increase at level 1 is a lot. Perfect if you want to kill Roshan at level 1 or if you want to simplify early ganks and lane kills: particularly, playing with an Ursa is the best way to make it work because of constant Roshan kills and the Overpower ability (which removes the drawback of Chilling Touch.
Maybe make this into an "underrated heroes" section instead of "underrated supports"? Just for the content, it can help a lot in drafting.
Witch Doctor isn't picked much because he does not have "the best stun in the game", his W heal is hard to sustain while being a support AND using your other skills efficiently, his E is hard to land and his R is nice but it's chanelling and is mostly single target.
This post just shows how balanced of a game dota 2 is. nice work.
EDIT: Oh, and consider adding Bane, Keeper of the Light, support Kunkka, Leshrac, Lich, Lion, Shadow Demon, Shadow Shaman, Treant Protector and Vengeful Spirit (assuming you want to keep this as "supports only" drafting tips.
I like AA, but he's pretty situational, really needs a good trilane to be effective. Cold Feet is fantastic if you can land it, but can be shrugged off by many heroes and powers. I especially like him against Clockwerk as Power Cogs can become a liability for him, also Alchemist.
Disruptor - massively effective against certain offlaners ( Dark Seer, Windrunner, poss Mirana). If they get even vaguely out of position after level 2 then their escape won't be much help.
[{Witch Doctor]] - remember this being discussed a while ago, he has some great attributes, but is quite needy in terms of backup/equipment compared to most supports. Also squishy as hell. However, I think he makes a great 4 in the right situations, e.g. paired with armour reducers, some hard carries etc.