Dinged 89-90 on my priest last night in under an hour. Wtih rested the bushes of swarminglings on the timeless isle will award approximately 500k XP. They are extremely slow moving, grouped up and do only minor posion damage.

There are 5 bushes they don't respawn immediately but fast enough to make it more efficent than any other method. Plus the mobs drop lesser charms, and the boa loot.

Previously used spots such as Dooker Dome appear to have been nerfed.

Another way to level from 89-90 quickly is to get a friend with a 2 person mount to help you get all the treasures from http://www.wowhead.com/achievement=7997. Should take approx 30mins and it gives about 12 million XP and also about 2k gold.