Shadow Shaman - Honestly I think you'd have to be borderline retarded not to win with a Shadow Shaman on your team. His ult means if you can get to a tower, you essentially take that tower. He has a combined 8.5 second disable/stun and he has a Q burst damage spell that can deal as much as 2240 total damage over 7 targets. He is CRAZY good and I'm surprised he doesn't get more love.

Tiny - Once he gets the necessary items and levels, he can just swat enemy teams out of existence with his aghs tree. My favorite carry.

Slardar - I like him in general, but he's my go-to pick against invis heroes, especially ones like Riki or Clinkz who have very low survivability to begin with. Pop your ult on one and you get true sight of him for 25 seconds, plenty of time to take him down.

Treant Protector - Another hero who doesn't get much love but I think he is a prototypical support. He has an invis spell that he can use on himself and allies, a DoT spell that damages them and heals you, a healing/armor spell that allows you to heal towers, a massive group stun, AND with aghs you get a spell that gives you unlimited free wards for the rest of the game. Oh, and he's a natural tank with the highest natural DPS in the game. I am puzzled that no one picks him.

Ogre Magi - Really good support who's hard to kill and can be extremely effective in ganks, teamfights, and even (lategame) one-on-one. He fits multiple roles and picking him reveals very little to the other side about your team composition.

Necrophos - I take him against tanky heroes like Pudge or Axe. Two of his best spells, his aura and his ult, both rely on health percentages rather than hard damage numbers, which means they scale better when facing tanks. If Axe has ~4000 HP, my teammates only have to get him down to around half of that and suddenly my ult can deal him the rest of the ~2000 dmg, AND he spends more time dead.