One of my favorite areas to farm in Diablo 3 is the Fields of Misery in Act 1. Since my Monk is now level 56 in Hell difficulty, I will center this discussion around what you can expect to gain from farming this zone on Hell. You can obviously farm it on Nightmare or Normal and I suspect it will be very popular in Inferno.
Fields of Misery is the zone right after defeating the Skeleton King, which makes it fairly easy if you have made it so far. It gets easier as you find or buy upgrades.
To get there, the best thing is to select the quest "Khazra Den" from the quest interface. Take the highlighted waypoint and exit through the north cemetery gate whereupon you'll find yourself in the Fields of Misery. Proceed to clear the entire area methodically, including (and especially) all the random dungeons you may encounter.
Make sure to complete the Khazra Den quest because it is very easy (the mobs inside are pushovers, plus no nasty random bosses) and it gives you some nice XP. Also make sure to turn in the quest once you are done farming the area, for another XP reward. Now, if you are 60, this doesn't apply, of course, so feel free to skip this quest.
The cool thing about the Fields of Misery is that there are a bunch of dungeons and random events that spawn and, on every run I have undertaken, there were no less than 3 of these. Each of them gives nice loot in the form of drops from rare spawns or even more loot from Resplendent Chests. Here are the ones I have encountered.
This is your cookie-cutter 2-level mini-dungeon with a few champions/rares inside and a Resplendent Chest at the bottom.
Another 2-level mini-dungeon with a shitload of zombies inside. The zombies are very good for XP because the Spewing Horrows keep puking them so if you want you can even avoid killing these lady-zombies and let them puke zombies over and over again.
On level 2 there's a Resplendent chest and a small quest given by a ghost. She asks you to kill 3 elites that spawn but they're very easy, just watch out for the frozen orbs they sometimes summon. The reward for the quest is very puny, just one blue item. Oh and make sure to clear the room before starting this quest, as you don't want hordes of zombies to assault you while you're killing those elites.
The Secluded Grove
There's a Resplendent Chest in the middle of this grove with a rare elite tree called The Old Man who attacks you when you approach. As you fight him, 3-4 other trees spawn. It's a very easy fight, just make sure they don't surround you because you won't be able to escape their vicious poison. I died stupidly on my Monk due to this and my overconfidence.
This is a tiny area on the north side of the Fields of Misery which spawns a single room inside a cottage called Pillaged Home. As you get close to the entrance, a Moon Clan Warrior bursts out the door and you can enter the house after killing him. The small room inside has a Bloody Chest and a bunch of lootable dead bodies.
This is a farm with a farmer who hands you a quest to destroy 4 Plague Nests. Another easy quest. It only gives a little XP and gold as reward.
Another farm quest. As you approach this area you'll find the body of a large beast on the ground. Clicking on it will start the event. A bunch of Burrowing Leapers spawn followed by a rare Leaper named Burrow Bile. They are an easy kill. After dispatching them talk to the farmer and he opens up his cellar to you. Enter it and you'll find a Resplendent Chest. Also watch the dialogue between the farmer and his "wife". It's hilarious.
There's also a very rare house which spawns in a tiny area called Lonely Dwelling. The house is called House of Curious and has a merchant inside who might sell rare weapons and rare dyes.
Thoroughly clearing the Fields of Misery with all the dungeons takes between 30-40 minutes. At level 56 it rewarded me with a total of 427K XP, or a little over 1/5 of the experience required for the next level.
I made on average 37K gold from drops and from vendoring all the junk I found. I also got 2-4 rares regularly each run, despite having only 8% magic find. Check out these pants, for instance, which were a very nice upgrade and something that I couldn't even find on the AH for a decent price.
Apart from this I also found 4 Tomes of Blacksmithing and 6 Tomes of Jewelcrafting, as well as 5 Radiant and 3 Square gems. You can figure out the market price of these on your own. Easily a few thousand.
This is one particular run that I recorded exactly but all my runs were very consistent in terms of rewards.
I highly recommend farming Fields of Misery if you've reached a point where Act 2 feels a bit too hard and this is valid anywhere from Normal to Inferno. OK, Normal is a bit too easy so you probably don't want to waste a lot of time there. One word of caution: all the underground dungeons have 2-3 packs of champions or rares inside. You were expecting that weren't you?
Have you farmed Fields of Misery? Know of any other nice farming spots?