Stake

A stake is a sharpened piece of wood that has supernatural properties and can be used as a weapon.

Wooden Stakes
Stakes made of ordinary wood, dipped in the blood of a certain victim, can be lethal to Tricksters. Sam and Dean attempt to kill the Trickster in "Changing Channels" by stabbing him with a wood stake dipped in an imaginary victim's blood. When the stake fails to kill the Trickster, the Winchesters deduce that they are not actually dealing with a Trickster.

In "Hammer of the Gods", Dean uses a wooden stake to kill Zao Shen.

Palo Santo stake
A stake made of Palo Santo ("Holy Wood") from Peru can immobilize demons as demonstrated by Tamara in "The Magnificent Seven" when she uses it to stop a demon possessing the corpse of Isaac.

Evergreen stake
These stakes will kill certain Pagan Gods, as seen in "A Very Supernatural Christmas" in which Sam and Dean use such weapons to kill Madge and Edward Carrigan.

Cypress stake
A Cypress stake is a wooden stake made from the branch of a Cypress tree found in Babylon. It's the only thing that can kill the Whore of Babylon. However, it must be wielded by a true servant of Heaven in order for it to work.

In the Season 5 episode "99 Problems", Castiel acquires a Cypress stake from Babylon to use against the Whore, who is trying to condemn the inhabitants of a town to Hell. Neither Castiel nor the Winchester brothers consider themselves to be true servants of Heaven (Castiel and Dean have both openly defied Heaven, and Sam is an "abomination"), so they give it to the town's priest Pastor Gideon instead. However when the group confronts the Whore of Babylon, Gideon drops the stake in the struggle that ensues. Dean picks it up, and although both he and the Whore are convinced it won't work, he stabs her though the chest with it. Surprisingly, it works and the Whore is killed. The Cypress stake is incinerated in the process.

The fact that Dean was able to kill the Whore - thus qualifying as a "true servant of Heaven" - makes Sam worry that he's going to give in to the Archangel Michael.

Olive wood stake
An 1000 year old Olive wood stake carved by vestal virgins and dipped in the blood of something ("you don't want to know") can be used to kill the god Chronos. (Time After Time)

Trivia

 * Cypress is a general term given to a variety of trees found in the Mediterranean.
 * In mythology and other popular culture, wooden stakes are used to kill Vampires. However, this is not the case with the Vampires in Supernatural.