Sunan An-Nasai compiled by the the great Imam An-Nasai has the fewest weak ahadith after the two Sahih collections and contains 5761 ahadith, making it as an invaluable addition to ahadith collection.
One of the six most authentic collections of the Ahadith which has 4800 Hadith (selected from a mass of 50,000) divided into many different subjects, each Section containing many Hadith.
His compilation of this Sahih comes second only to Sahih al Bukhari in terms of authenticity according to majority of scholars & is the second in the collection of 6 books called "Sihah Sittah"
With 3956 ahadith, Jami' At-Tirmidi is an invaluable addition to any person's library of hadith collection. It is also considered as the most authentic among the Four Sunan
Indeed it would be no exaggeration to say that to this day most traditional hadeeth scholarship is directly or indirectly based on this work of Ibn Salah
Chain of Command is a course regarding the Sciences of Hadeeth where author covers the Scholars of Hadith (Muhadithoon) and the actual science of scrutinizing and analyzing hadeeth
One of the greatest compilations of the Sunnah and books of Hadith, the Musnad by Imam Ahmad bin Hanbal, organized into compilations of the hadiths narrated by each Companion.