The Argent Tournament is part of the new content coming in patch 3.1, and it was sort of a surprise when it was announced the other day, just before the PTR came up. We hadn't heard anything about it previously, not even any hints at its addition, so it grabbed our interest right away.
We had to check it out, of course. There are a few quests you can do right off the bat, but they're not particularly exciting. The first two quests you pick up are just some gathering quests. It gets a little more exciting from there, but I was honestly much more interested in the visuals of the event. While there's obviously a lot of development still happening there (lots of placeholder tags), what is done looks really awesome. When this event goes live, I have no doubt we'll see a lot of people going back to using their racial mounts once these new skins have been added in.
Just south of the tournament, there also seems to be a failed Frost Wyrm resurrection site, a Death Knight's blade jutting out of the ice with a wyrm just below the surface. I wish we knew the story behind that!
Screenshots of the new mounts, tabards, banners, and the whole shebang are in the gallery below. Check it out, and if there's anything you want to see in greater detail, leave a comment to this post and I'll see what I can do for you.
Gallery: Patch 3.1: The Argent Tournament