Progression

So this is the advised progression when Burning Crusade first came out. Since then, additional, more difficult dungeons have been released such as Black Temple, Zul'Aman, and the Sunwell stuff.
The best advice would be, at this point, don't move on to something more difficult until you are sure you've gotten everything you need from the current set of dungeons.

So to Aaron and Dave, our next official instance should be Sethekk Halls, followed by some rep grinding. Lets also look into getting the Arcatraz Key. I've always been curious about that place anyway.