I've already done the murloc, but there are a few other WoW monsters I think are really cool.
My list would be:
The quillboar, a humanoid porcupine-boar that is very destructive, but also pretty cool.
The cloud serpent, which is a winged snake. Very mexican-oriented, but really fun.
The makrura, which are intelligent crabs.
Maybe on the goblin tradesmen. They are a heck of a lot of fun (and my character is a goblin), but I don't think they really fit into the typical D&D game.
Many WoW monsters are very similar to existing D&D monsters, but these stand out to me.