Shock Trooper Feat
You can also take Improved Bull Rush as a fighter (with all those extra feats, why not?

), and besides getting a +4 bonus on your bull rush attempt against a defender, you're set up for the tactical feat Shock Trooper, in Complete Warrior, which let's you do any of the three following things:
1.-
Directed Bull-rush: When you start a bull-rush, for every 5 feet you move an opponent, you can move them an additional 5 feet to either side. This is good when you've got a wall and past that there's a cliff to one side, so you can push them forward and then towards the cliff.
2.-
Bull-rush Tripping: You can push an opponent to a square occupied by another foe, and you get a free trip attempt against both of them, and they can't trip you if you fail the check. Coupled with Combat Reflexes it can be a deadly combination. You leave them prone, and then you get both AoO's against them, with a +4 to hit them.
3.-
Heedless Charge: This is my favourite. When you charge, you must use at least 5 points of Power Attack, and subtract them from your AC instead of your base attack. Your great-sword or great-axe wielding fighter or barbarian would begin to maul all your enemies. Granted, he would be a sitting duck for a whole round, but he'd get a very high amount of damage if he hits, which is very likely, and that's the very function of the power-attacking barbarian, it's what they all seek

.
Branok.