I meet a Nunu, Alistar double jungle... ruined my whole game as jungler. maybe you should add him in one of the tiers?

Nice troll build to mix things up. We usually play Tiamat Tuesday (all go boots + 5 Tiamats) and have never lost a game. That doesn't make it a viable strategy or "META". Neither is double juggling because it so easily countered. Heard of CV? First time you invade enemy side you will face an 2vs3 or 2vs4 (depending on top/bottom) where you both die - end of game.

However, fun troll build to play time to time, maybe on Wednesdays :)

So you steal their red, they steal yours. End of the story.

I think it's too risky now. Especially against a premade team.

Rememeber : if you are premade, they are too ...

I think that Dragon and Ganking are important enough to deserve their own sections respectively.
Some information on when to dragon and when not to (i.e. their mid is dead) and how to avoid having dragon stolen from you as well as how to steal it would be nice(warding, cv in the right place). It's better to use skills such as Smite and Consume when dragon is getting low to avoid a steal, as well.
A little bit of information on ganking will go a long way too, you could probably mention that since your ganks should almost always be 2-man, it takes coordination for both players to land their cc and that you should probably tell your parter beforehand ('hey, I stun first').

I would also like to see Leona, Skarner, Riven, and Shyvana added as potential duo jungle canidates.
Leona clears pretty well with another champ due to the fact that her passive is now being proc'd by her partner in the jungle. She brings pretty much insane cc and decent burst damage to ganks with her skill combo and passive procs. She is mana-hungry and needs blue most of the time, though, so she synergizes well with junglers that don't need blue buff and/or have spammable aoe (to proc her passive). Leona can be built pure tank by maxing her w first or an offtank that does decent damage by prioritizing q over w and buying a sheen/trinity.
Skarner clears pretty fast and has some sustain via Fracture, and his ultimate is pretty much godly when it comes to ganking. He also as a fairly good slow on his q and does pretty good damage with just a sheen and can be built pure tank after his trinity.
Riven is pretty much the queen of early game ganks which duo junglers will miss out on, but the fact that she does not need blue buff, has four gap closers and an insanely fast jungle clear time with her skill+AA spam does make her a good duo jungler, especially a partner that can stun/snare/fear the enemy long enough so that Riven can get close enough and pretty much melt face.
Shyvana has basicly the FASTEST JUNGLE CLEAR TIME in the entire game and does not need blue buff, but lacks cc--which a duo jungling partner can make up for.

There is a problem though, as most jungle heros are tanky and lack damage output compared to other champions and the 2v1 lane goes to a tank which he will lose horribly as a support+AD carry combo is hard to beat in a lane--therefore the only one dealing significant damage is your AD carry. This is a pretty risky strategy as the solo top in the current meta can just choose to build anti-carry and take your AD out in every fight and keep him underfarmed if the two tanky junglers and your laning tank aren't competent enough to peel him off the AD and due to a lack of an AP carry, your team will have a game where early game your duo junglers are severely behind in levels and when they catch up by mid game, the other team will almost always be ahead and that can cause problems as the other team can group push before the duo junglers get to gank with their ults, screwing over your team. I do think that duo jungling is an awesome thing, but it needs improvement.

Let it be known that Taric/Sion DOMINATES double jungle. Taric's heal = godlike sustain, double stun = godlike ganks, double AOE = godlike everything. And if they find the enemy jungler its GG.

I think this is a great new meta you've discovered. I'm also sure RIOT has seen this guide, due to their recent patch to increase neutral monster spawns.

However you are missing some pertinent sections that would generate the +1 from me.

- Include a section on enemy solo junglers (i.e. who to be careful of, how to counter them, etc.). I have encountered an enemy duo jungle while jungling alone with Shaco, lets just say their efforts were in vain.

- Include a section on map awareness. I see you have an entire section on warding. Map awareness is much more than just sticking a few wards on the map and calling it good. In a lot of pubs, your team mates are probably too busy looking for last hits, or watching their health bars to notice the flicker of an enemy champ coming up river about to gank them. Since there are two people in the jungle, go over how you/your jungle partner can help by keeping a constant eye on that little minimap.

- I love the Nunu and Warwick builds, and they work wonderfully in tandem in the jungle. Try adding more duo jungler examples to increase this meta's popularity.

Other than that this general guide is pretty solid, and definitely expandable. Great job so far, I look forward to your updates.

Could you reevaluate shen, now that he has been massively buffed?

I havnt updated the tiering in awhile but will do so again once dominion comes out or another couple champions.

I was wondering your thoughts on using Skarner as a double jungle champ.

Great extensive guide, now all I need to do is find someone who wants try it out with me xD

this actully worked well. noct and ww in dubble=win. then we use zilean mid, cho top, and nunu bot. with this set up u can take baron at 15 min.

Yeah if they have an enemy jungler doing this just destroys their team if u can pull it off right.