Some Useful Sources for the Study of Nahj al-balagha

The Nahj al-balagha is one of the most influential texts in Shi'i Islam and it is esteemed also in many other parts of the Islamic World. It is a collection of speeches, letters, and sayings attributed to 'Ali b. Abi Talib. It was compiled by al-Sharif al-Radi (d. 406/1016). What follows is a non-comprehensive list of sources for the study of this work. I may update it irregularly, and people are welcome to suggest additions.