I was thinking. There really isn't all that much support for a fighter to use two weapon fighting.
So I suggest the addition of a few feats, and a lot of fighter only feats.
First
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Perfect Two-Weapon Fighting
Prerequisites
Base attack bonus +16, Greater Two-Weapon Fighting, Improved Two-Weapon Fighting, Two-Weapon Fighting.
Benefit
You can make as many attacks with your off-hand weapon as with your primary weapon, using the same base attack bonus. You still take the normal penalties for fighting with two weapons.
Normal
Without this feat, you can only get a single attack with an off-hand weapon (or two attacks with an off-hand weapon if you have Improved Two-Weapon Fighting, or three attacks with an off-hand weapon if you have Greater Two-Weapon Fighting).
*Fighter Feats:*
Two Weapon Rend
Prerequisite: Fighter Level 6, Two Weapon Fighting
Benefit: When ever you deal damage with both weapons in both hands you deal an additional 2d4 damage. The damage type is the same as your off hand weapon.
Perfected Two Weapon Fighting Balance
Prerequisite: Fighter Level 9 or Base Attack of +12, Two weapon fighting
Benefit: You reduce the minuses to fighting with two weapons by 1. You also treat a one handed weapon as light weapons for the purposes of two weapon fighting.
*Modify Weapon Finesse*
Special
A fighter may select Weapon Finesse as one of his fighter bonus feats. When a fighter reaches 9th level this feat also includes all one handed weapons as being able to use the fighters dex instead of str as a bonus to hit.
Natural weapons are always considered light weapons.
Improved Two Weapon Rend
Prerequisite: Fighter Level 12, Two Weapon Rend, Two Weapon Fighting
Benefit: When ever you deal damage with both weapons in both hands you deal an additional 2d6 damage. The damage type is the same as your off hand weapon. This damage is in replacement of the normal 2D4 damage of two weapon rend and do no stack.