Demented Shaman has a multi-heal that he can cast almost constantly this is great in group battles, but also works out really well for just pushing a lane down; it heals allies and hurts enemies within range. Great support hero. He also can put a shield on allies that, when they are attacked, causes their health regeneration to go up drastically. He can also slow enemies and reduce their armor.
Also, Nymphora is a great support hero as well, she can heal and restore mana. She can also teleport to any part of the map, and with Staff of the Master she can pull allies to her.
There is Ophelia... but I wouldn't suggest her, really... just something to look into if you like.
But the ultimate would be Jeraziah. He is a tank. Can heal, cause immunity to magic damage (but that stops him from being able to heal that person temporarily), and can make all surrounding ally heroes immune to physical damage with his ultimate. Hook him up with a ring of sorcery and you'll always have mana to be casting. He is the best of the support heroes IMO and can easily change the outcome of any match if played well.
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