Powerful Charge

 
Prerequisite(s): Base Attack Bonus 1+, Medium size or larger
 
Benefit: When you charge, if your melee attack hits, you do an extra 1d8 damage if you are a medium creature. Larger creatures do additional damage as follows: Large:2d6, Huge:3d6, Gargantuan:3d6, Colossal:4d6. This feat can only be used when charging, it does not work if you are mounted. If you have the ability to make multiple attacks on a charge, only the first attack gains this bonus.
 
Source: Monster Manual 3, Miniatures Handbook, Eberron Campaign Setting