WoW Horde Leveling Strategy

0-15 - Questing fastest possible exp.
15-20 - The Barrens - Harpies
15-20 - The Barrens - Bristleback(s)
20-25 - The Barrens - Bael Dun Exavs
20-25 - Hillsbrad - Hillsbrad Farmers (etc)
22-26 - Thousand Needles - Galak Scouts (etc)
26-30 - Hillsbrad - Mud Gnolls
25-30 - Thousand Needles - Grimtotems
30-38 - Shimmering Flats - All monsters.
38-40 - Dustwallow Swamp - Very North East Islands, Murlock Warriors/Oracles.

Horde And Alliance Grinding Spots:
40-46 - Feralas - Woodpaws (stay away from the ones that disease for slow casting speeds)
46-48 - Feralas - Frayfeather Skystormers
48-50 - Feralas - Harpies
48-51 - Southwest of Gadgetzan - Thistleshrubs
50-54 - Western Plaguelands - First 'field' to the left, assorted monsters.
54-60 - Western Plaguelands - Scarlet Lumberjacks
52-60 - Eastern Dire Maul - Lashers

Recommended

EXP Rates:
Levels 30-40 = 18-20k exp/hour
Levels 40-51 = 20-25k exp/hour
Levels 52-60 = 40-50k exp/hour (Dire Maul)

Power Leveling

This is the method the power levelers have used since closed beta and I finally got one of them to give it up. It is by no means the way to go if you want to maximize your experience in the game as this method will bypass almost all the content in the game and essentially ignore many of the fun, unique aspects of WoW. This is not recommended for new players and is meant for players who already have experienced the content and just want to level up an alt to play with their level 60 friends (ie. your level 60 instance group needs a priest and there are no priests to be had). As a benchmark to how successful you are with this, download cosmos (Cosmos) and use the clock feature to measure your xp/hour. At level 50 you should be getting about 40,000+/hour. 1-20: Newbie lands, stick to the friendly zones (not contested). Just grind. The quests are a waste of time up to level 20 if you are focusing on maxing out xp per hour. 20-26: Wetlands quests and raptors/slime/orcs for grinding. Redridge mountain Lakeshire quests.

26-30: Duskwood quests and undead for grinding. Hillsbrad critter roamers for grinding.

30-35: Did these all in a day on Daggerspines in Hillsbrad right next to Southshore along the coast. Huge spawn, very fast respawn rate, easy mobs to kill. Purgation isle (island in the very far Southwest water area of Hillsbrad) also a nice secluded place you can grind on undead.

36-40: Hillsbrad southshore quests. Desolace quests and kodo grinding for 36-38, then Undead Ravagers in the southeast for 38-40. Cresting exiles at the circle of outer binding in Arathi also for 37-41; extremely easy mobs with a fast respawn. Alterac ogres from 35-40 for grinding. Drywhisker kobolds in Arathi east of Hammerfall for 36-39 for grinding.

41-45: Hinterlands trolls, owl beasts, and wolves for grinding and quests. Badlands ogres, gnolls, and quests.

45-48: Tanaris quests and pirates on the eastern paninsula for grinding. Stranglethorn vale quests (only if you need rewards imo). Badlands greater elementals for grinding.

48-52: Felwood deadwood gnolls for grinding and quests from the sanctuary in the south. Blasted lands dreadmauls for grinding. Un'goro crater (best started at 50) for primarily quests and grinding off the plants and tar elementals. Azshara undead highbornes and thunderhead hyppogriffs for grinding.

52-55: Azshara blood elves for grinding. Burning steppes dreadmaul rock ogre caves firegut ogres (very low AC) for grinding. Felwood irontree woods and cave for grinding (great spot). Western plaguelands questing for argent dawn and grinding on undead throughout the various camps.

55-58: Eastern plaguelands quests from the sanctuary, grinding on undead at the ruined towns. Winterspring grinding at winterfall village or Lake Kel'Theril undead highbornes (my personal favorite camp). Blackrock Stronghold in Burning Steppes for grinding.

58-60: "The" yeti cave in Winterspring, due Southeast of Everlook (very nice place). Grosh Gok compound ogres in Deadwind pass (great spot, no one knows about it). Eastern plaguelands Fungal Vale undead grinding and argent dawn token farming. Moonowls in northeast winterspring for grinding.

10-13 Dreadmaw Crocolisks in the river between Durator and Barrens. 14,000 exp per hour

13-16 Southsea Bandits and Cannoneers south of Ratchet. 14,000 exp per hour

16-19 Theramore Marines outside Norwatch Keep. 16,000 exp per hour

19-22 South Barrens Stormhides and Quilboards. 18,000 exp per hour.

22-24 Bears and Spiders right outside Tarren Mill. 20,000 exp per hour

24-26 Centaur north of Freewind Post in 1,000 Needles (outside the cave) 20,000 exp per hour (lots of mining opportunities; Tin, Iron)

26-30 Centaur north of Freewind Post in 1,000 Needles (inside the cave) 20,000 exp per hour (lots of mining opportunities; Iron, Gold, some Mithril)

30-32 Roguefeather Harpies inside cave on south wall of 1,000 Needles. 20,000 exp per hour (lots of mining opportunities; Iron, Gold)

Note: The Kurzen areas are generally considered broken now; especially for Horde on PvP servers. But it's all I currently know at this level as the spot was so good at the time, that is all I did from 32-42.

32-37 Kurzen camp in North Stranglethorn Vale (outside cave) 26,000 -32,000 exp per hour. This actually got better as I went up in level as long as no one else was at the camp. At level 36, I tested about 1/4 of the level and my experience rate was 32,640 per hour when I had to stop and go sell.

37-42 Kurzen camp in North Stranglethorn (inside cave) 29,000 - 34,000 exp per hour; 5-7 gold per hour. Go in past the Kurzen Commandos and Kurzen Headhunters to the Elites and Witchdoctors. The Commandos have armor, and stun you when they are low on life, so they are poor experience, but the Elites and Witchdoctors inside are the same old no-armor experience givers. I told my guild this area is just a leveling field with juicy experiene berries waiting to be plucked. I'm currently 39 here, and still doing full levels in just about 2 hours of grinding.

I didn't grind as exclusively from here on out, so I'm going to shotgun a few spots and level ranges that felt "Good". I still measured exp per hour, but this was just after the last patch where they upgraded armor and HP on most monsters I grind on, so exp definitely slowed down.

42 - 45 Woodpaw Gnolls in Feralas, south of Camp Mojache. Stay away from the Trappers and Brutes IMO, and head further south to the Mystics and Reavers. I liked the area that was still on flat land with a couple of Alpha camps on raised mounds. I usually avoided the alphas as they tended to be bugged/grouped in a cluster of 3. Spell disruption is a must for the Mystics. I cleared about 24k exp per hour here typically.

42-44 Ogres in Feralas. Due north of camp Mojache in the mountains. The Mages are best if you have spell disruption, but I worked through all of them and they were all good experience. The Brutes will throw you, so make sure they don't throw you into an add. 20-24k exp per hour.

44 - 47/48 Dustbelcher Ogres in the Badlands. Now here is a good spot, and it may be good on PvP as well. I camped this cave for 3 hours one Saturday without seeing another player. The cave is in the Southwest corner of the bladlands past a bunch of Ogres. The reason why I say the cave, is that it's about 75% Ogre Mages, and if you have spell disruption, they go down easy. Very low hp and low armor even after the patch. The only reason I left at 48 is I could clear the spawn too quickly, and I wanted to do Tanaris quests.

48-52 Dunemaul Ogres in Tanaris (great Mageweave drops). I like the NE ruins for the early levels, as I could move around it in a circle. Once I got to 50, I liked the higher density in the actual Dunemaul Compound area.

52-56 Western Plaugelands. The field with the Skeletal Slayers right by the Bulwark. Great Runecloth drops, and actually I prefered to kill the melees here over the casters (casters seemed to have the same HP and armor as melees). I've been pulling 26k exp per hour or better here.