Daily Quests are repeatable quests that can be done daily. They are scattered around all over The Outlands.
Isle of Quel'danas located north of Silvermoon City is a whole entire island dedicated to daily quests.
Some daily quests require you to do a chain of quests to unlock them.
Example: Threat from Above
Below are some mobs that hand out Daily Quests.
Daily Quests mobs will have a Blue exclamation point (!) over their head.
Note: these are not all of the mobs for daily quests.
For more information on the various daily quests check out our Wiki guide @ Daily Quests Guide.