So barbarian gives you Strength and Constitution; bear warrior gives you both but more. Assuming you still want to avoid multiclassing, feats are your only real options. Those probably should look something like this:
City Brawler bonus feats: Improved Unarmed Strike, Two-Weapon Fighting
Human bonus feat: Improved Grapple
- Extra Rage
- Power Attack
- Improved Bull Rush
- Shock Trooper
- Improved Two-Weapon Fighting1
- Greater Two-Weapon Fighting1
- Versatile Unarmed Strike2
1 These feats require a lot of Dexterity. It’s entirely possible that you won’t have and won’t want that much Dexterity. In that case... more Extra Rage, I guess.
2 Or anytime earlier if you feel you’re running into a lot of such DR.
That gets you five rages per day, your unarmed strikes can deal a variety of damage types, and at the end you get a lot of attacks in a grapple. But your grappling will be only mediocre, your attacks are not going to do particularly high damage, and Shock Trooper is only thrown in there because it’s a decent feat that will make you at least not entirely useless when you can’t grapple.
Some multiclassing options
If you can multiclass, you should. Barbarian does not offer much at all from 3rd to 7th level. If nothing else, you can take fighter levels to free up more feats to take Extra Rage, so the one significant bonus at Barbarian 4 can actually be done better without barbarian levels.
You don’t really need feats all that badly, but several of the feats you’re taking are fighter bonus feats, which means you can take them with a couple levels of fighter and take Extra Rage instead. You can also snag Combat Reflexes if your Dexterity isn’t awful, so you can take an attack of opportunity, and with Improved Grab, start a grapple then-and-there.
But fighter should really never be taken for more than two levels. A feat per level is OK, a feat every other level is awful.
The advantage of ranger is that you can get Improved Two-Weapon Fighting as a bonus feat (ignoring the Dex requirement, even!), and then take Favored Power Attack from Complete Warrior, which at least makes your Power Attack useful against a couple of types of foe, and the Distracting Attack variant from Player’s Handbook II, to help the rogue out against enemies you can’t grapple. You also get a lot of skill points and a couple of spells, to make you less of a one-trick pony. The idea here would be Barbarian 1/Ranger 6/Bear Warrior.
Horizon walker is a core prestige class (i.e. technically it’s from Dungeon Master’s Guide not Player’s Handbook), but you can squeeze two levels of it in before qualifying for bear warrior. It requires Endurance and 8 ranks of Knowledge (geography), so it works best with at least three levels of ranger.
The big advantage of horizon walker is the desert terrain mastery. That gets you immunity to Fatigue, which means you can end your rage early without becoming fatigued until the end of the fight. Plus you’re immune to other sources of fatigue and exhaustion results in fatigue, instead, which is nice because fatigue is bad and exhaustion is awful.
For the second level, underground’s 60-ft. darkvision is almost certainly your best choice; a +4 competence bonus to a skill is just not all that exciting.
After you finish bear warrior, returning to horizon walker long enough to get a planar terrain mastery means you can take the shifting mastery, i.e. the ability to use dimension door once every 1d4 rounds. Dimension door is far from a great spell, but it is teleportation which can be difficult to come by for a martial character. The cavernous mastery’s 30-ft. tremorsense isn’t bad either, though by that level you really need to have gotten into the air.
Ideal build is probably just Barbarian 2/Ranger 3/Horizon Walker 2/Bear Warrior 10.
This class from Complete Warrior is not great. Its curse is Charisma-based, which is fairly awkward for you (could try to be intimidating, I guess), and what it does isn’t all that great. But it is full-BAB, has a good Will save which is useful to you, and the arcane resistance and mettle class features are decent. But what really makes this worth even considering is Player’s Handbook II, which offers one variant on it that makes it useful to you: the dark companion.
The dark companion replaces the familiar, and provides a 3×3 square area of −2 to AC and −2 to saves. It’s just an illusion, and it’s painfully vulnerable to dispel magic, but those penalties are pretty significant. It can move independently of you, and has pretty big range.
Effectively, it allows you to serve two roles for your party: locking one enemy down with your grapple, while making another enemy vulnerable to attacks and spells.
That takes four levels, barbarian takes two. The last level should be fighter for feats or ranger for skills.
This is a weird option, but I kind of like the story it tells: a knight who lost his civility and nobility, becoming savage and warmongering. Sounds neat, anyway. You start as a knight from Player’s Handbook II, take it for three levels to get bulwark of defense, and then change alignment, forsake knight, and go to barbarian. You lose the knight’s challenge features, but you maintain the Mounted Combat bonus feat (though you’ll probably never use it), shield block +1 (which you’ll definitely never use), and bulwark of defense (which you definitely will use).
Bulwark of defense makes you “sticky”—people next to you will have a hard time becoming not next to you. Less useful since presumably you’ll be grabbing them, but your grappling won’t exactly be stellar so this provides a decent back-up for things you can’t grapple.
Three levels of knight and two levels of barbarian still leaves two levels. Ranger remains probably the best option, just for the skill points (Favored Power Attack maybe if you can pick a foe you really will see all the time), though fighter could work for feats. A fourth level of knight gets you armor mastery (medium), which is OK if you want to go with mithral full-plate as your armor.