SRD:Halberd

Description
If you use a ready action to set a halberd against a charge, you deal double damage on a successful hit against a charging character.

You can use a halberd to make trip attacks. If you are tripped during your own trip attempt, you can drop the halberd to avoid being tripped.

A halberd does either piercing or slashing damage (player’s choice at time of attack).