I apologize for posting this in a new thread, wasn't aware that there was a thread for this. Anyway.
NOTE: You can also get behind the little "caged" areas in the sewers. (With the rats/meat.
I joined this forum January 15th 2007, and since then I have actually contributed 0 content. I am proud to say that I actually discovered something that (hopefully) hasn't been posted yet, and (hopefully) can help some people out!
Jumping around Dalaran this evening and discovered another way to get under the Dalaran arena! This works AFTER the 3.3.3 nerf.
Anyhow, instead of trying to explain the glitch though text, I figured I'd throw together a quick video. Enjoy!
[ame=http://www.youtube.com/watch?v=G0sxZFHAcJI]YouTube - How to get into the Dalaran Arena (AFTER 3.3.3 NERF!)[/ame]