The quests to open up Sons of Hodir rep dailies.

All the phasing quests really. Pretty much everything in Icecrown.

I liked the concept in Culling of Stratholme too.

The questline with Drakuru might be worth doing if you like storylines (the one that ends in Drak'tharon Keep).

As the dude with the bizarro glasses said, do them all. I did and there are some fun ones and some dull ones, but worth doing 99% of them. I think Zul'drak was my least favorite zone.