For those who take Bear Warrior and don't want to bother going an extra 5 levels for Dire form which only grants an additional +4 Str mod, there is an alternative:

Warshaper, also from Complete Warrior. While it only has d8 HD, and worse, you loose 2 BAB from it, there are certain compensations, such as immunity to Critical Hits (and thus sneak attacks) and Stunning at 1st level, an extra size increase for natural attacks at level 2, extra reach at level 3 (so those spiked-chain barbarian guys can just weep with envy because you don't need no stinkin' chain to do the same thing).

Really, a 3 level dip is the best. This only loses you 1 BAB, a couple of hit points, and you can still go Barbarian7/BearWarrior10/Warshaper3, and be perfectly viable.

However, for a Warforged Barbarian who goes Bear Warrior, you gain an additional advantage for going 4 levels: Fast Healing while shaped. This is big, because otherwise Warforged have a hard time finding healing.

So for a Bear Warrior Barbarian, a 3 level dip in Warshaper can be extremely profitable.