Lion is a good support, but I really like Dark Seer.
I find that, so long as the person playing him has an IQ of >80, he is impossible to fuck up. Four castables, amazing jungler, great ricer if he needs to be.\
Shell the carry.
Surge the carry. (half your shit is done with two clicks)
Put down your ulti wall. (can be done to varying degrees of effectiveness)
Vacuum tactfully. (again, this can make or break a fight)
But still, if you at least cast your stuff, 80% of the time you will help. A lot. He's a great support and really gets unrecognized as an introductory Dota 2 hero.
@Hutchoo: that was my first game with Medusa in Dota 2 xD I had a lucky game.
(yes, I do enjoy playing Medusa if you're wondering about my game history)