You could consider instituting the stunt system from the
Book of Iron Might, written by Mike Mearls and published by Malhavoc Press. It's a D&D-supplement version of what he did with his OGL game
Iron Heroes, in many ways.
The first chapter introduces combat maneuvers, which basically offer a way to devise special attacks which are generally balanced with existing options in the core rules. For instance, in the core D&D combat system you can make a trip attack, which requires a Strength check and exposes you to the same effect if you fail. In the combat maneuver system, the trip effect (render your opponent prone) would carry an attack penalty of -10, for argument's sake. You don't want to be taking -10 on your attack roll just to trip someone, so you add two drawbacks (make Strength check, can be tripped if you fail) which each reduce the penalty by 5 to a total of 0 - and you have your trip attack.
The range of maneuver effects and drawbacks is pretty wide - ability score damage, daze attacks, forced movement, knockback, an immobilizing ranged attack that pins your foe to the wall, for instance, with the maneuver drawing attacks of opportunity, causing the effects only and no damage, requiring a full-round action, or needing such overwhelming effort that you lose your footing and fall prone.
Whether you create a set of standard maneuvers or allow players to create them on the fly depending on the present circumstances is up to you. The other great part is that maneuvers have "warning flags" calling out possibly unbalanced situations that can arise, so that you're warned of consequences you might not have intended.
The other great section of the book for this situation is the stunt system in the fourth chapter - which uses base attack and skill checks, often combining two skill checks together in the same action, to pull off daredevil stuff to give you an edge in combat. When fighting giants, for instance, the Climb stunt "Scaling Attack" could be useful - you climb up a much larger opponent to deny them their Dexterity bonus to AC from your attacks. There are plenty of stunts useful to barbarians - the Survival stunt "Wilderness Tactics" which uses the natural environment to your advantage, the Intimidate stunt "Blood-Kissed Threat" to render an ally of a foe you just dropped shaken - as well as more free-form uses of skills to pull off stunts in combat.
The stunt system includes a "DM Judgement Factor" in determining skill check DCs so as to set the right tone for the campaign's action. Normally this would be no bonus or penalty at all, but in a low-stunt, realistic campaign there might be +5 to the DC so that only the truly athletic can really pull off stunts, while in a swashbuckling campaign that's all about the daring moves there might be a -10 to the DC.
I highly recommend the
Book of Iron Might to anyone who wants more options for warriors in D&D. It also includes some other excellent material which isn't directly relevant to this topic - arcane battle feats which grant supernatural enhancements in combat (including
wuxia standing on air and flying), battlemind feats for the intellectual, meditative warrior, and fighting style feats which grant minor techniques as your character improves in martial ability (gains base attack bonus).
There's also an interesting construct race which is
much more a "fantasy robot" than the warforged.
