This block took me the longest amount of time to get through, you will feel that hitting level 50 is forever out of reach. It is important to keep focus at this point in the game. Honestly this is where things are going to get boring if you do not focus on quests.

Instances in this block are the way to keep moving. There are 3 to get you through and that is Scarlet Monastery, Uldaman and Zul'Farrak. Scarlet Monastery will keep you going strong until you reach level 45. Now there are plenty of quests and the experience is good in these instances. If you once again focus on running them more than 1 time, you will see progression and you may ever surprise yourself by leveling.

Azshara off of Ashenvale is one area you can hunt out of. The downside to this zone is that it feels unfinished and there are only a few quests to work on. I have seen many other players grinding in this zone though. I asked a few players why they hunt in Azshara and they informed me that they get the most cash and experience to get them through. It is not a very dangerous zone and the risk vs reward is decent.

Badlands is still ripe hunting grounds up until around level 45, as is Dustwallow Marsh.

Many quests can be found at the neutral city in Tanaris and that will keep you going for 3-4 levels easily before things slow down.

There are also Alliance quests running out of Feathermoon Stronghold in Feralas.

One area you can focus on grinding experience is in Tanaris by hunting Wastewander Bandits a little to the east of Gadgetzan.

Once you hit level 46 you can head over to the Hinterlands for more questing and experience.