Portrait Pals is a selection of little pets I've attached to your player unit frame. It varies based on your class and is purely cosmetic.
Death Knight - Frostwyrm Welp
Demon Hunter - Soul Crystal
Druid - Baby Moonkin (Faction-specific)
Hunter - Fenrir
Mage - Phoenix
Monk - Emerald Dragon (Pandaria)
Paladin - Tyriel Pet
Priest - Naaru
Rogue - Crow
Shaman - Earth Pebble-mental
Warlock - Floating Skull
Warrior - Shield (Safeguard spell, this one was hard!)