Leveling to 90 the fastest

AD: If you haven't been in beta, or didn't study the leveling paths deeply all the way to 90, there's an update available to Zygor's leveling guides. It supports 1-90 leveling now and is by far the fastest way to reach level 90, beating no-sleep dungeon grinding by miles. It's available to both the Horde and Alliance, and supports all races all the way from their starting point.

All of the Zygor Guides have an
user fiendly ingame interface.

Fastest player boosted through 1-85 in less than 2 days. Getting 5 additional levels takes less than a day!

While hundreds of other players are struggling with quest objectives, new achievements and reputations, all you have to do is follow the ingame waypoint arrow that points you to the next step of whatever guide you are using.

There's currently Leveling, Reputations, Titles, Professions and Achievements guide for Mists of Pandaria.

Zygor is a paid addon, but there's a free trial available so you can use it for free and check it out if you like it or not.