Hearthpwn

I'm not going to promise you Legendary with this deck, but what I will promise you is barrels of fun.  It can be a little slow, but if you mulligan right you can hold them off till it really starts to ramp up with some crazy combos.  Pretty much every minion has death rattle, so the Baron is superb in this deck.  

I have about a 70% win rate with this deck in the 12-20 ranks, but I haven't gotten a chance to really work any higher than that.  Hunter's a pretty bad match-up so I imagine getting passed that rank 5+ hunterfest I keep hearing of will be near impossible.  

Other hilarious combos include:

KT+Ancestral Spirit.  Double KT ftw.

Sylvanas+Reincarnate

Baron+Thaddius Twins

Frankly, by the time you get to turn 5 or 6 you'll have some sort of crazy combo in your hand.

Early mulligan strat:

A turn 1 crypt keeper is ideal always.  Eggs and ghouls are also a priority.  Slapping a rockbiter or defender of argus on the eggs are a great way to pump out those 4/4's as wells  as get some removal going.  Depending on the class you are facing, lightning storm can be a great choice.