At a glance:






I played a bit of Ubers in Gen IV (my older brother was the one who REALLY liked it, and he got pretty high on the ladder), and as I switched from Gen IV OU to Gen V, I learned just how much I hated weather wars. Sure, stall was pretty irritating in Gen IV (I ran an anti-lead to stop SR and a rapid spin Starmie and a few other anti-metagame tricks), but I had not experienced true misery until the advent of Politoed.
So as I ragequit the OU tier, I figured I'd base most of my team around the Ubers team I ran in Gen IV. Of course, it didn't transfer all that well, and after a series of modifications, this is what I wound up with. It's basically a very offensively oriented team (as most of Ubers is) with Skarmory there as a check to the rampant dragon moves and also as an important check to ExtremeKiller Arceus (or virtually any variant, really) and also, of course, to set up entry hazards.
In-depth analyses

Skarmory (M) @ Leftovers
Trait: Sturdy
EVs: 252 HP / 4 Def / 252 SDef
Bold Nature (+Def, -Atk)
- Stealth Rock
- Spikes
- Roost
- Whirlwind
As I understand it, this is mostly fairly standard for Skarmory in Ubers, so I won't go into too much detail describing it here. It is an excellent dragon resist and all-around incredibly difficult to kill. Even enemies sporting fire moves often have difficulty in the rain. I included both Stealth Rock and Spikes because I have no other decent source of Rocks, so Skarm has to provide both. Usually, it does a pretty good job. It also works to counter virtually any form of Arceus, and it usually gets a free layer of Spikes from the most common form, the ExtremeKiller.
Having a designated lead does not really work in Gen V because of the team preview. However, I use Skarm to lead a lot if I think the foe is going to lead with pretty much anything physical, such as Groudon (which is fairly common). They'll either switch it out as I get free rocks, or they will try to do something about it, which usually lets me get up more without taking more damage than I can simply Roost away.
Garchomp (M) @ Choice Band
Trait: Sand Veil
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Earthquake
- Outrage
- Stone Edge
- Dual Chop
While it is less common to run Garchomp without Sand Veil hax support, I like it quite a lot. It's generally assumed by the opponent that Garchomp is running a Choice Scarf rather than a Band, so they usually switch in something that can't quite take the hit. As an example, Outrage is often a 2HKO on Groudon (depending on its EV spread), and usually OHKO on 0 HP 0 Def Kyogre (definitely with Rocks up). So this thing packs a punch. The least standard thing on this moveset is probably Dual Chop which I run to take out Subs or the rare Haban berry. I originally had it as Crunch, but I found virtually no uses for it, and it seemed much better to have a non-locking Dragon move. Stone Edge, of course, is for Ho-Oh and Lugia.
I run Garchomp as a lead sometimes if Skarm isn't going to work, such as against Kyogre. Honestly, this is not that good of a plan, but I really don't know what to do against Kyogre leads since they're so often Choiced but not often enough to rely on it.
I used to have this slot filled with a Scarfed Darkrai, which I used most of the time as a lead just to put the Kyogre to sleep even if it was Scarfed, but, unfortunately, Darkrai's typing was not what I needed; I had absolutely no Pokemon that resisted Electric, and Zekrom and Thunder from Kyogre were a significant issues.

Mewtwo @ Life Orb
Trait: Pressure
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Aura Sphere
- Ice Beam
- Psystrike
- Thunder
This Mewtwo, along with Kyogre and Rayquaza, were directly stolen from my brother's Gen IV team. Mewtwo is fantastically fast, more durable than one would expect, and got a great new weapon in the form of Psystrike for Gen V. Actually, that was the one change; the previous Mewtwo ran Selfdestruct as a huge shock to special walls that came in; it's not even necessary any more. Unfortunately, I think the Timid nature is necessary to outspeed a lot of threats, most notably enemy Darkrai, which Mewtwo can OHKO with Aura Sphere.
This is not a particularly complicated set. Mewtwo comes in and attacks things. The things it's attacking die. It does fairly well against Arceus because of Aura Sphere, especially if they are the Steel or Rock Arceus variants meant to counter the ExtremeKiller. Ice Beam, of course, hits the majority of Ubers for at least 2x damage, and Thunder is very helpful in the rain. Although, I'm less sure of Thunder now since Psystrike already does plenty of damage to enemy Kyogre. I'm considering changing Thunder out, but I'm not sure what would be better; perhaps Grass Knot for a guaranteed OHKO on Groudon or maybe the rare Gastrodon? The thing is, nobody in his right mind uses Groudon against Mewtwo anyway, and Gastrodon is not something one generally takes into account when designing Uber teams. I also considered a fire move for threats such as Ferrothorn, but that has awful synergy with my deliberate attempt to set up rain.

Rayquaza @ Life Orb
Trait: Air Lock
EVs: 252 Atk / 6 SAtk / 252 Spd
Hasty Nature (+Spd, -Def)
- Dragon Dance
- Outrage
- ExtremeSpeed
- Overheat
Rayquaza has been one of my very favorite Pokemon since its release in Gen III. After a single Dragon Dance, he outspeeds virtually any threat that is going to dare enter the field and can OHKO anything without a resistance (or anything called "Groudon with defense investment") with an insanely powerful Outrage. Steel types often switch in while the Dragon Dance goes off only to find that Overheat is not nearly as fun as they might have initially assumed. Among the biggest threats to this set is Choice Scarf Palkia, which takes a maximum of 77.3% of its health from a +1 ExtremeSpeed and otherwise outspeeds Rayquaza and kills it. Fortunately, Palkia is often baited into attacking Kyogre, which generally results in its death.
A common scenario is that Rayquaza comes in free of a teammate KO, gets a Dragon Dance on the switch to the Steel type, and then Overheats and proceeds to wreck everything. Well, maybe not everything, but it is nice to get the Ferrothorns of the world out of the way. It's also very important to have a fire move on a rain team uninhibited by the weather. On a similar note, Rayquaza functions as an excellent check to things like Kingdra and Excadrill which otherwise are major hassles in their respective elements. Usually any Excas come in on Mewtwo and hope for an easy X-Scissor kill but instead get destroyed by Overheat. I'm honestly not quite sure why that isn't commonly expected to be run on Rayquaza, but as far as I can tell, people rarely see it coming.

Kyogre @ Leftovers
Trait: Drizzle
EVs: 236 HP / 252 SAtk / 22 Spd
Modest Nature (+SAtk, -Atk)
- Calm Mind
- Ice Beam
- Thunder
- Surf
Calm Mind Kyogre is my personal favorite of Kyogre sets. Sure, Specs is fun, but being locked in isn't. I gave the Kyogre a couple of Speed EVs out of HP to outspeed other base 90s that happen to come against me, even if they gave theirs a little bit of speed for the same reason. I don't think the 4 HP will be that sorely missed since I am not making substitutes.
Basically, the premise is to get a Calm Mind or two and then absolutely destroy anything you can manage to hit. Palkia switch in to kill this set VERY frequently; if there's a Palkia on the team, I can bet it's going to switch in. However, Palkia actually loses if I get a Calm Mind in while it switches. Two +1 Thunders are enough to take down Palkia, but Palkia can't do enough to 2HKO Kyogre with its Thunder. This does, however, put a major dent in Kyogre; a switch to Garchomp is also an option. Usually they won't go with a Dragon move because after they see the Calm Mind, they realize failing to do damage could be quite detrimental. Unless I feel a particular need to keep the Kyogre healthy, however, I usually just kill the Palkia. If it has residual damage already (one Stealth Rock hit is usually enough), then using Calm Mind again puts Kyogre high enough to OHKO and take less damage from the Palkia's second Thunder.
One major concern is a Mewtwo's revenge kill Psystrike, which is not a fun experience for Kyogre. Skarmory, of course, can take that easily, but Mewtwo almost always carries Thunder or at least Fire Blast, the former of which is more than plenty to kill Skarm. Unfortunately, Skarmory does not have any easy switch-ins out of an enemy Mewtwo because they also use Aura Sphere and Ice Beam on Skarmory if they're not carrying anything more damaging, and sometimes even if they are. Usually at that point I sacrifice something with lower HP or sometimes Skarm unless I know something about the Mewtwo already.

Arceus @ Lum Berry
Trait: Multitype
EVs: 6 HP / 252 Atk / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Swords Dance
- ExtremeSpeed
- Shadow Claw
- Earthquake
Any Ubers team without an Arceus is doing something seriously wrong. The number of ways this can be utilized are just ridiculous, and about half of them are to counter other Arceus forms. Mostly this one, actually. ExtremeKiller is the most common variant, and for good reason. Left unchecked for just one turn, +2 ExtremeSpeed wrecks most things.
I don't know how common it is to see a Lum Berry (I think it's usually a Silk Scarf, Life Orb, or Leftovers), but it works wonders. Most checks rely on taking a hit and then burning Arceus, such as most opposing non-Extremekiller Arceus sets and both Giratina forms. Fortunately, Arceus has time to get up +2 against these as they switch in. In the case of Rock and Steel Arceus, a +2 Earthquake is either a OHKO (or veeeery close) or they invested enough into both HP and Defense that they can't outspeed you. Either way, they only get a chance to activate the Lum Berry and die. Ghost Arceus can be OHKO'd by a +4 Shadow Claw, but it often runs a +Speed nature and cannot be OHKO'd by +2 Shadow Claw, nor can it be finished with Extremespeed after. Great Wall Giratina also is a problem for Arceus because it can't even be killed by a +4 Shadow Claw and can phaze it out with Dragon Tail after burning, or even before. Fortunately, Skarmory is there.
So that's my team. Any advice would be appreciated; it isn't quite as solidified as I'd like. Some of the biggest weaknesses that have been bothering me are lack of a Rapid Spin user or Spinblocker. I have considered using Forretress with SR, Toxic Spikes, Rapid Spin, and maybe Payback or Gyro Ball, but I do not want to lose Skarmory's ground immunity, reliable recovery, and phazing ability. Further, Forretress has a much worse weakness to fire than Skarmory does; Skarmory's is even neutralized in the rain. I also really liked Scarf Darkrai, but I really needed the electric immunity badly. It occurs to me that it could replace Mewtwo, but honestly, I think Mewtwo is better than Darkrai. Thoughts?
EDIT: I just looked up my ranking; I'm currently 23rd on the Smogon server with 1262 points. However, I'm not sure how much this means because I have been doing this for under a week, and the change to Garchomp occurred probably only a couple of days ago.