Zombie Villagers are similar to Zombies in texture and AI, but instead of a zombified Steve head, they have a zombified Villager head. They have a small chance to spawn naturally, but are also created when a Villager is killed by a Zombie. They can be "cured" (turned back into a villager) by giving them a Golden Apple and a Potion of Healing (needs confirmation). Like Zombies, they will pick up and, if possible, equip items from the ground. They can spawn as Infernal Mobs.
For the most part, they have the same drops as Zombies (Rotten Flesh, Potato, Carrots, and rarely weapons/armor), but instead of dropping a Zombie Head, they have a rare chance of dropping a Villager Zombie Head.