We all are in a constant search for new markets, aren't we? Analyzing the competitors is the obvious way to go. Here is what I do when I am bored by gold making routine.
Check the competitors on the Undermine Journal
If you are like me, playing on a US or Oceanic server, the Undermine Journal (TUJ) is always your best friend. I like to check periodically what my major competitors are selling and see if I can find anything to add to my own list.
Watch the combat log
I have a bunch of alts and sometimes use them to spy on my competitors, standing next to them and reading a combat log. You can use this method even to watch characters of the other faction. Nowadays, when Dalaran is empty and the auctioneer is located conveniently right near the profession suppliers, it is a nice place to do crafting and selling. One of my characters is based there too, making things, posting auctions and watching one of the competitors from the other side, who probably think that I am not online.
Pay attention to visual effects
To explain this last point I will tell you my story about discovering a niche market.
One day I was chilling in one of the major cities and saw a visual effect that I have not seen since the beginning of Cata but it was very familiar. Someone was making Moonshroud and the pillar of light made him stand out of the crowd. (I remember back in Wrath I always went out of the city to make these special kinds of cloth). I checked the guy on TUJ and the only thing he was selling were Emerald bags. That is how I found a new market. If that person had known how I did it, probably he would have tried to hide somewhere too.
Sorry, I have to go. One of my competitors just came to Dalaran and is crafting something.
Have a nice day!