World of Warcraft features several in-game holiday events that can cause mini markets with special items that attract attention during these times only. The best example of this is during Winter's Veil, which runs from mid-December until New Years. During this event, Small Eggs become high in demand as they are needed for a cooking recipe related to an achievement of the event. While the profits from this example may be slim, look out for similar opportunities for all of the game's holidays and events, such as:
Lunar Festival
Love is in the Air
Noblegarden
Children's Week
Midsummer Fire Festival
Brewfest
Hallow's End
Pilgrim's Bounty
Winter Veil