World of Warcraft hacks and exploits aren't necessarily cheating, just fun and sometimes profitable "special cases" that players have found while adventuring. Here are a few that you can try for yourself.
See Mob Weapon Drops Before they are Killed
This WoW hack is for the Alter of Storms (and maybe other places) in the Blasted Lands. The monsters that spawn there seem to have a bug with weapon drops. If the mob is going to drop a weapon or offhand item you'll see them carrying it around instead of their normal default staff, sword, etc.
You can use this to scan around for epic drops! Both the Glowing Brightwood Staff and Krol Blade have the potential of dropping here so there's big gold to be made picking out and killing the right mobs! Just run around scanning the mobs and if one is holding a Glowing Brightwood instead of their boring staff or sword you're guaranteed the staff when you kill it!
(This also proves that loot is pre-determined when the mob is spawned instead of allocated once there is a corpse.)
Sell your AH items for above normal price
Not exactly a World of Warcraft exploit but a good way to use player's greed against them and make some extra gold quickly. First you must actually have an epic / blue you wish to sell. Put it in the auction house for a much higher than normal price using an alt then advertise that it's up on the trade channel (eg Glowing Brightwood Staff in AH – 500 gold (normally goes for around 250 gold)).
Log onto your main a few minutes later and advertise that you want to buy the item – eg WTB Glowing Brightwood Staff! Will pay 700g!
People are so greedy they will go to the AH and buyout your staff and / w you that they will sell you it for 700 gold.
Next say someone is already going too sell you one and you just sold an epic for a higher then normal price easily, quickly and in a non-scamming way. This isn't a WoW hack or WoW exploit but it works like a charm!
Easy Warrior Weapon Skillups
The trick is to find an undead skeleton or ghost type mob that's immune to Rend. Charge them and continuously rend. It will be immune but it will still count as a swing and you will still level up the skill. You will also keep your rage because the mob is immune and be able to continuously rend without needing to do any damage. Therefore allowing you to do it an infinite number of times, until your weapon skill is max.
Change Your Character's Name During Realm Transfer
This is old but I put it here for the people that don't know. If the character name already exists in the realm that you wish to transfer, you will be given the option to select a new name. So simply create a new character with your current name on the realm before you start the transfer.