Hi,
The method I used for getting to 90 as soon as possible and without having to quest much is this:
1. Go to Kota Basecamp at Kun-Lai Summit.
2. Go up the mountain to the southwest.
3. Find the cave with the yetis inside.
4. Pick up about 100 of the berries lying around.
5. Macro the berries to an ability you often use.
6. Kill yetis. I've found the bottom room to be better, but you can run back and forth.
As a blood dk, I changed my dual spec to frost so I could kill these faster and I could kill 2 or 3 every minute with the buff from the berries. Each gives about 35k exp at 88 and 31k exp at 89. If you can dispel their enrage, they will get a debuff quicker and will take 30% more damage.