Two-Weapon Defense( Player's Handbook v.3.5, p. 102)
[Fighter Bonus Feat, General]
Your two-weapon fighting style bolsters your defense as well as your offense.
Two-Weapon Fighting (PH) , DEX 15,
Improved Two-Weapon Defense (CW) ,
When wielding a double weapon or two weapons (not including natural weapons or unarmed strikes), you gain a +1 shield bonus to your AC. When you are fighting defensively or using the total defense action, this shield bonus increases to +2.
A fighter may select Two-Weapon Defense as one of his fighter bonus feats.