Improved Shield Bash( Player's Handbook v.3.5, p. 96)
[Fighter Bonus Feat, General]
You can bash with a shield while retaining its shield bonus to your Armor Class.
Shield Proficiency (PH) ,
Agile Shield Fighter (PH2) , Shield Charge (CW) , Shield Slam (CW) , Shield Sling (PH2) ,
When you perform a shield bash, you may still apply the shield's shield bonus to your AC.
A fighter may select Improved Shield Bash as one of his fighter bonus feats (see page 38).
Without this feat, a character who performs a shield bash loses the shield's shield bonus to AC until his or her next turn.