Recent successes:
When I started playing Zoo already meant Demon Zoo, so I thought I'd try something more classical.
Power Overwhelming x2
Voidwalker x2
Flame Imp x2
Abusive Sergeant x2
Haunted Creeper x2
Dire Wolf Alpha
Knife Juggler x2
Nerubian Egg x2
Ironbeak Owl x2
Dark Peddler x2
Imp Gang Boss x2
Defender of Argus x2
Dark Iron Dwarf x2
Implosion x2
Loatheb
Doomguard x2
It's pretty strong, and is also cheap for a Warlock deck. Zoo is aggressive, but isn't a face deck: the idea is to take control of the board and never let it go. You have PO and Doomguard for some burst to close out games, but don't be afraid to use them to make favourable trades.
If you want something crude but effective, try this variation of Secret Paladin:
Noble Sacrifice x2
Competitive Spirit
Avenge x2
Redemption
Repentance
Haunted Creeper x2
Knife Juggler x2
Shielded Minibot x2
Muster for Battle x2
Coghammer
Aldor Peacekeeper x2
Piloted Shredder x2
Keeper of Uldaman x2
Truesilver
Sludge Belcher x2
Loatheb
Mysterious Challenger x2
Dr Boom
Tirion
You cut out the inconsistent 1-drops to stuff it full of high value minions. Midrange Druid lost steam for me at rank 3 this season, but this list powered straight through to legend in a few hours.