All lockpicking levels listed below are when the item first becomes "orange", you may pick the locks on them until it is no longer beneficial to do so (turns grey, better options, etc)

Battered Junkbox - 25
Worn Junkbox - 100
Sturdy Junkbox -175
Heavy Junkbox - 250
Strong Junkbox - 300

Stuff from random drops
Ornate Bronze Lockbox - 60
Heavy Bronze Lockbox - 75
Iron Lockbox - 85
Heavy Iron Lockbox - 125
Steel Lockbox - 180
Reinforced Steel Lockbox - 225
Mithril Lockbox - 225
Thorium Lockbox - 225
Eternium Lockbox - 225
Khorium Lockbox - 325

Doors
Gnomeregan - 150
Scarlet Monastery - 175
Searing Gorge Gate - 225
Blackrock Depths - 280
Scholomance - 280
Dire Maul - 300

Footlockers

The lockpicking skill levels for these start pretty close to the lowest typical mob found in the zone x5. For instance a level 20 zone would have footlockers that you could pick at 5x20=100 lockpicking skill. I don't have accurate listings of when these become orange so if you have additional information please feel free to submit!

Hillsbrad Foothills - Durnholde Keep - 75?
Redridge Mountains - Lake Everstill - 75?
Ashenvale Forest - Zoram Strand - 75?
Stonetalon Mountains - Windshear Crag and Associated Mines - 75?
Wetlands - Murloc Camps - 100?
Desolace - Sar'theris Strand - 175?
Badlands - Angor Fortress 175?
Swamp of Sorrows - Pool of Tears - 200?
Searing Gorge - 200?
Tanaris Desert - Lost Rigger Cove - 225?
Azshara - Bay of Storms - 275?
Eastern Plaguelands - Tyr's Hand - 275?

The Guide - Horde and Alliance
To start out with there is a slight difference in the beginning of lockpicking for Horde and Alliance but eventually it will come on the same path so I will start them out separately.

Horde Lockpicking 1-85
Once you get the quest for lockpicking there are chests inside of a ship near Ratchet. It's the only ship in the water that's not sunken so you can't miss it. Inside the ship is what the quest refers to as a "place where they train their thieves" and that's exactly where you want to head. You can pick the locks on those chests until about 85 skill. There is also a chest in there for the Polly quest that has a pretty decent respawn timer that you could pick to increase your skill as well although I've never stayed at it passed 100 you may want to use that as an alternative instead of the next part.

Horde Lockpicking 85-175
You will get a quest for your poisons, you may not know it as your poisons quest but the objective is to pick pocket a key, kill some things , kill a boss(elite), and open his chest. You will do this northwest of Sludge Fen. You get the quest at 20 but it is highly unlikely you will be able to complete it till 24+, I'd wait until you were 26ish. The end guy is an elite who will beat you down every single time you try this quest, in order to keep picking the lock on his chest to skill up you will have to kill him every spawn. I've never been able to do this quest below level 24 with any of my rogues, so good luck to you! This chest can bring you up to 175 if your patient, I usually leave in the 150's though.

Alliance Lockpicking 1-85
Alliance also get similiar quests as compared to the Horde. The thieves training area this time is by Atler Mill northeast of Lakeshire. You can stay at these chests until about skill 85, but keep a watch out for horde while you're in Redridge, they seem to camp the area.

Alliance Lockpicking 85-175
The Alliance poison quest happens in a tower that is northeaster part of Westfall. The actual tower is located to the east of bridge that heads to darkshire. The quest is very similiar to the Horde, there is a chest in the top that you can pick to about 175, but you first have to find a way to incapacitate or kill the elite boss to make it worth while. I wouldn't try it unless you're 24 plus and that may be hard for anyone who isn't geared up or twinked well.

Both Lockpicking 175-225
This part can be tricky. The way I would do it though is to go pickpocket sturdy junkboxes (use allakhzam to lookup where they come from, I think the Ogres in Tanaris have them) and get your lockpicking skill to 180. Once you hit a lockpicking skill of 180 then I suggest going to Scarlet Monastery and picking all of the doors. The ones outside the instance are on a timer so you can only do those a few times every so often, but hit up all the doors on the way in, go into an instance, unlock more doors, open chests, and pickpocket junkboxes all the way to 225.


Both Lockpicking 225-280
You could do the Searing Gorge door but it's not a reliable way to skill up, so you're pretty much stuck with doing junk boxes. At this point what you could also do is open lockboxes for free in a big city and get your skill up that way. You'll probably be getting more instance groups too and those tend to have at least one locked chest per instance. See the above list for doors and items in this skill range.

Both Lockpicking 280-300
There are doors in Blackrock Depths that you can pick, otherwise continue istance runs, pick pocketing, and advertising opening lockboxes for free. Make sure you use the above chart for guidance it what items you should be looking to picklock so you don't waste time.

Both Lockpicking 300-375
There are several ways to go from 300-375. The Boulderfists can be pickpocketed in Nagrand for Strong Junkboxes. Khorium Lockboxes are random dropped in the Burning Crusade zones but mostly found in the new Burning Crusades instances. The Dire Maul doors are also an option to get a few skillups. Going from 1-375 is no easy task and will take a lot of time, but it will definately payout in the end