Angel Blade
A weapon capable of killing angels. It is could be described as a long blade, or a short sword. It is referred to as the Sword Of Lucifer in the official episode summary released by The CW, although it is never referred to as this in canon.
Initially in Uriel's possession, Anna used it to kill him. It is possible Castiel obtained it when Anna was captured and taken prisoner by Heaven.
4.16 On The Head Of A Pin
Uriel, a supporter of Lucifer is trying to recruit angels to his cause, which is to help free Lucifer from hell. When they refuse Uriel kills them with the Sword of Lucifer. Eventually Anna uses it to kill him.
5.01 Sympathy For The Devil
As Zachariah tries to coerce Dean in agreeing to be the Archangel Michael's vessel, Castiel arrives, and attacks the angels with a blade which kills them. It appears to be the same blade used by Anna although this is unconfirmed.
5.13 The Song Remains The Same
Castiel carries the blade with him when he meets with Anna. It is also one of the items that Castiel puts in the bag he gives to Sam before they travel through time. A young Mary Winchester will then use this blade to defend herself against Anna, but it is knocked out of her hand. According to Uriel, only an Angel can kill another angel. But since Castiel gives his blade to the Winchesters to use on Anna it could be surmised that this blade is usually only carried by angels, yet that doesn't mean it is not effective in the hands of a human.
