SRD:Dagger of Venom

Dagger of Venom: This black +1 dagger has a serrated edge. It allows the wielder to use a poison effect (as the spell, save DC 14) upon a creature struck by the blade once per day. The wielder can decide to use the power after he has struck. Doing so is a free action, but the poison effect must be invoked in the same round that the dagger strikes.

Faint necromancy; CL 5th; Craft Magical Arms and Armor, poison; Price 8,302 gp; Cost 4,302 gp + 320 XP.