I need a 1 level dip

[Invader]

For the werebear build I've been working on I'm going barbarian 4, warshaper 4 (flashmorph won't be useful as I'll be in bear form most of the time anyway).

Is there anything that would make a really good 1 level dip with minimal prerequisites that's better than just taking a 5th level in barbarian?

[Urpriest]

Fist of the Forest might be very nice. You're likely to already have Improved Unarmed Strike and Power Attack, so basically you'd be trading Great Fortitude for Con to AC (while unarmored, but since you can't make use of the Wild property, unless you're going with barding you're likely to be unarmored anyway), fast movement, a mini-rage, and a boost to unarmed damage.

[Djinn_in_Tonic]

Fighter gets you a bonus feat, and is a standard 1-level dip. Warblade is also a decent 1-level dip class.

[Vizzerdrix]

Cloistered Cleric is always a superb 1 level dip if you have access to complete champion. Travel and knowledge Devotions are always useful.

[eggynack]

Well, two levels of fighter are pretty universally better than getting the third and fourth levels of barbarian. Trading away trap sense is an obviously good idea, no matter what you're doing, and if you're going for the 1/day rage, extra rage exists as a feat, and you're pulling half that. You're basically getting like three rages over your usual amount per day, even though extra rage isn't a fighter feat, and even though you probably won't take it twice. That's just how build math works. Anyways, ToB dips are classically good, as are totemist and cleric dips.

[Biffoniacus_Furiou]

If you go with one of the Barbarian variants (http://www.d20srd.org/srd/variant/classes/variantCharacterClasses.htm#barbarianVariantTotemB arbarian) you can get a more useful class feature at Barbarian 5. Improved Uncanny Dodge is still decent, though.

A level of Warblade or Crusader can be useful, especially since you can count half of all your other class levels and those six Werebear hit dice toward your initiator level. Taking your 18th level in an initiator class won't catch you up to the usefulness of a spellcaster, but gaining options like Wall of Blades and Iron Heart Surge will certainly help.

[Hamste]

How high is your wisdom? You might want a monk dip just for the wisdom bonus (Though Monk's belt would probably be better). Frenzied Berserker is also a good dip (Make sure your mage has grease or something so you don't kill your allies) as it stacks with rage.

[Invader]

I'd love to take fist of forest but I'm not planning on taking any of the prerequisite feats which would make it kinda steep for a 1 level dip.

[Helcack]

Taking 1 level druid will give you some awesome stuff if you can convince your DM to let you use variants.
Druidic Avenger+Deadly Hunter:
Druidic Avenger:(neg Animal Companion)
Gain Rage 1/day(As you already have this I suggest switching it out for Whirling Frenzy, allowing you to have your normal rages+Whirling Frenzy 1/day)
+10 movement speed(Now you are at 50 woohoo!)
You can't cast Summon Nature's Ally spontaneously
Deadly Hunter:(neg Wild Shape and proficiencies you don't need)
Wis bonus to AC whilst unarmoured
Favoured Enemy
Track feat
Swift Tracker

In addition you can use Druid wands without UMD and you have access to three 0 level spells and two(if your Wis is 12+) 1st level spells which I suggest allocating as follows:
Toolbox:
0 Detect Magic, Create Water, Flare
1 Obscuring Mist, Climbing Tree
Healer:
0 Cure Minour Wounds x3
1 Vigor, Lesser x2
Melee:
0 Virtuex3
1 Instant of Power x2

HP, BAB, and Saves Druid 1 vs Barbarian 5
HP: d8 vs d12(Barbarian)
BAB: +0 vs +1(Barbarian)
Saves:
Fort +2 vs +0(Barbarian)
Ref +0 vs +0(Barbarian)
Will +2 vs +0(Barbarian)