There are 19 new pets to collect including the new Raiding with Leashes set  from Burning Crusade.

Raiding with Leashes II: Attunement Edition

Collecting all 10 pets from Karazhan, Serpentshrine Cavern and Tempest Keep will reward you with Tito.

Tito

Karazhan
Lil Bad Wolf

Lil’ Bad Wolf (Spiky Collar) – Drops from Opera Event (Big Bad Wolf)

Menagerie Custodian

Menagerie Custodian (Instant Arcane Sanctum Security Kit) – Drops from The Curator

Fiendish Imp

Fiendish Imp (Satyr Charm) – Drops from Terestian Illhoof

Netherspace Abyssal

Netherspace Abyssal (Netherspace Portal-Stone) – Drops from Prince Malchezaar

Serpentshrine Cavern
Tainted Waveling

Tainted Waveling (Tainted Core) – Drops from Hydross the Unstable

Tideskipper (Shell of Tide-Calling) – Drops from Morogrim Tidewalker

Tideskipper (Shell of Tide-Calling) – Drops from Morogrim Tidewalker

Coilfang Stalker

Coilfang Stalker (Dripping Strider Egg) – Drops from Lady Vashj

Tempest Keep
Phoenix Hawk Hatchling

Phoenix Hawk Hatchling (Brilliant Phoenix Hawk Feather) – Drops from Al’ar

Lesser Voidcaller

Lesser Voidcaller (Crystal of the Void) – Drops from High Astromancer Solarian

Pocket-Reaver

Pocket Reaver (Tiny Fel Engine Key) – Drops from Void Reaver

Other Drops/Purchase

Direhorn Runt

Direhorn Runt (Beast) – Drops from Direhorns on the Isle of Giants

Filthling

Filthling (Magic) – Drops from Quivering Filth on the Isle of Thunder

Gahz'rooki

Gahz’rooki (Aquatic) – Purchased from Ravika or Tenuki in Durotar

Throne of Thunder
Pygmy Direhorn

Pygmy Direhorn (Beast) – Drops from Horridon

Living Fluid

Living Fluid (Magic) – Drops from Primordius (LFR)

Viscous Horror

Viscous Horror (Magic) – Drops from Primordius in Throne of Thunder (normal and heroic)

Wild Pet

Unborn Val'kyr

The Unborn Val’kyr is the only wild pet to come out this patch and may be found all over Northrend. Capturing (or killing) one will affect the spawn rate of another appearing somewhere else on the continent.

PVP

Brutal Pet Brawler: Win 250 PvP pet battles through Find Battle with a full team of level 25 pets.