Horde progression through the new Azeroth

Solution 1:

MMO-Champion has posted this excellent map of the zone flow from 1-85 post-shattering:

A more detailed breakdown can be found at WoWPedia

In short, Eastern Kingdoms goes Tirsifal → Silverpine → Hillsbrad → Arathi → Hinterlands → Western Plaguelands → Eastern Plaguelands → Badlands → Searing Gorge → Burning Steppes → Blasted Lands.

Kalimdor goes Mulgore/Durotar → Northern Barrens/Azshara → Ashenvale → Stonetalon Mountains → Desolace → Feralas → Thousand Needles → Tanaris → Un'Goro → Silithus.

Alternately, you can jump off the path after Hillsbrad/Ashenvale, head to Northern Stranglethorn, and continue from there into Southern Stranglethorn, South Barrens, Dustwallow Marsh, before rejoining the Kalimdor path at Thousand Needles.

After completing Thousand Needles or Western Plaguelands, you again have the opportunity to jump paths, and can follow quests through Felwood and Winterspring instead, though you may need to hop back to Silithius and/or Blasted Lands to get the last few levels you need before Outland if you go that route.

Solution 2:

Here are some more diagrams, by WoWHead:

Source: http://www.wowhead.com/blog=174523/cataclysm-old-world-zone-changes#leveling-flow-changes

Solution 3:

And here as well are some maps done by Project CWAL, featuring zone names as well as levels: