Gestalt suggestions [3.PF]

[Tanuki Tales]

Short and sweet: What is a good candidate to gestalt with a Barbarian?

[bahamut920]

Incarnum classes are good (just avoid the Soulborn); Con as their key ability, most of their powers aren't actions and are perfectly usable in rage. You can create weapons out of thin air (or go the natural weapon route, if you want), shuffle skill bonuses around, and grant yourself abilities like pounce, flight, and displacement. If you've got the points to spare on Int (or some generous rolls), Factotum goes well with anything, although you'll have to cast your buff spells before raging (easy with Cunning Surge). Any class from Tome of Battle works pretty well, too. Maneuvers function normally during a rage, unless they require skill checks that you can't make while raging (IIRC, only Diamond Mind and Desert Wind are skill-check-heavy).

If you're looking for something a bit more Pathfinder, Alchemist works well. Using extracts is like drinking a potion (which you're still allowed to do during a rage, IIRC), mutagens can supply an alchemical bonus to Strength (good for stacking purposes) and have a long duration, and you have access to a decent amount of the buff and utility spells of a wizard, plus minor healing. Although there's a barbarian archetype that gets mutagens, IIRC; there's definitely one for both fighter and brawler. Path of War classes work as well as Tome of Battle ones, AFAIK.

[Gildedragon]

Binder or Warlock can be good as a way of a) shoring up your will b) giving you some out-of-combat abilities c) giving you some neat "magic" tricks to work with.
Warlock is pretty great as you can mix the warlock's melee style with the barbarian's fighting to get a pretty cool concept.

If you wanna be pure combat-y: Swordsage

[Gnaeus]

Summoner (Synthesist or otherwise). Gives the action economy of an entire extra guy, or a huge pile of HP and combat abilities.

Factotum (any class can use a pile of extra actions)

Any tier 1 class. Even if you can't use their abilities while raging, long duration buffs like magic vestment, greater magic weapon, bark skin and superior resistance help you fight. Then take some non combat spells for general utility, and a couple of always useful things like planar binding or Polymorph. Even if you never cast a spell in combat (and there will be fights where you should) the tier 1 classes are always a top option.

Failing those 3, path of war/ToB and incarna/akashic are always good choices.

[Aegis013]

Dragonfire Adept is also a potential consideration.

If PrCs are in the mix, Cleric/Elemental Scion of Zilargo 7 (Magic of Eberron I think) with Water Devotion feat and a water graft, and if you can take bear warrior on your Barbarian side and take any and all rage improving feats you can turn into a nigh invulnerable rampaging water bear using Elemental Merge.

Pairs well with Shape Soulmeld: Mask of the Threefold Chimera and Open Least Chakra feats from Incarnum since you'll be out of the world and in a water elemental when you take the backlash (thus avoiding it).

[digiman619]

Two classes that go well in gestalt are DSP's aegis and soulknife (NOT 3.5's soulknife; this one's actually useful and fun to play as). The aegis is a super flexible class that lets you create armor with your mind. Granted, these classes are psionic, but since they don't manifest, you'll likely be OK.

[frost890]

If your GM will allow you to bypass the alignment go with monk.

If not you can try ranger. This will give you a lot of skill points and a free weapon style(bow for range). The power attack train is what most go with when using a Barb.

Another option is artifcer. They are able to make things that will cover your lack of heavier armor. Rings, wands and amulets can all up your ac. It will also give you something to do when you are not in a rage.

[Krazzman]

I can vouch for Inquisitor. (Judgements, Skills, magic)
Oracle is always a solid option thanks to Rage Prophet (if the powerlevel of your group fits).

Hunter and Druid can also fit quite well if you make a sort of Rageshaper. Else Rogue (albeit a low option) can be quite awesome.

[Ualaa]

I'm in the midst of a Gestalt campaign at the moment.
I am the DM of the campaign, and we're in a place called Rappan Athuk, so I figured low mythic ranks, gestalt and slightly stronger than normal races were fitting.
Through 51 sessions, we have had 54 character deaths and five henchman deaths; we're 11th, having explored around 1/3rd of the dungeon.

One character was a mixture of primarily Druid and Barbarian, but had a small dip into Sorcerer.
That was primarily Mage Armor, most/all of the day, and a few castings of Shield for the first 'x' number of combats.

Wildshape into something, Rage, and pounce... it was rather sick as far as damage went.
High DPS, lots of hit points, defenses weren't atrocious but weren't stellar either.