Mandalorian Affiliations

Mandalorian Crusaders
this group was considered by many galactic historians to have been the first true group of Mandalorian shock troopers formed in the galaxy. The origins of the Crusaders have been traced back more than 5,000 years before the Battle of Endor, to a race of gray-skinned, apelike humanoid nomads that traveled through space seeking conflict of any kind. The Crusaders adhered to a loose set of laws known as the Canons of Honor, and were known to use state-of-the-art technology in their conquests. Religious historians discovered that the original Crusaders were a group of warriors dedicated to quasi-religious ideals, but over time, the Crusaders came to worship war and carnage. The Mandalorian Crusaders were known to have exterminated entire races, including the Kuarans, Fenelar, and Tlonians. Their love for war and combat drove them to participate in the Great Sith War, fighting alongside the Sith when an all-out attack was launched on Coruscant. However, the Jedi Knights managed to defeat the Sith, and nearly wiped out the Mandalorian Crusaders. The armor of the Mandalorian Crusaders was relatively primitive, when compared to that of the modern Mandalorian Protectors. This stemmed from the fact that the armor was worn for hand-to-hand combat more than blaster fighting. It was organic in appearance, with the shoulders and knees being studded with short spikes. The armor could be sealed for use in space, and was equipped with a Zim Systems rocket pack

Mandalorian Neo Crusaders
this was the name given to the first groups of beings who were recruited by the ancient Mandalorian Crusaders to join their ranks and fight alongside them in the Great Last Battle. These Neo-Crusaders became what many modern military experts consider the Mandalorian shock troopers, a collection of beings from disparate races and backgrounds who banded together under the tenets of the ancient Mandalorians. The armor worn by the Neo-Crusaders was much bulkier than that of their predecessors, but was designed to withstand blaster fire and to identify the wearer as a Neo-Crusader. This armor was not studded with weaponry, but was efficient and functional. Individual Neo-Crusaders painted their armor as they wished, allowing for a variety of color schemes. It was the Neo-Crusader armor that later became the design basis for the Old Republic's Senate Guards

Mandalorian Mercs
This was the name used by the survivors of the Mandalorian Wars and the Old Sith Wars to describe their loose brotherhood. After the combined forces of the Old Republic and the Jedi Knights virtually wiped out the Neo-Crusaders, the surviving Mandalorians were forced to go into business as mercenaries to stay alive. Disparate clans of mercenaries were formed under the guidance of the old Mandalorian Canons of Honor, but these new Mercs worshipped the credits in their bank accounts more than anything else.

Mandalorian Death Watch
this elite group of Mandalorian Mercs split off from the true Mandalorian shock troopers when Vizsla rebelled against the leadership of Jaster Mereel. It was believed that the Death Watch was destroyed at about the same time as the rest of the Mandalorians, during the Mandalorian Civil War, and their order became something of a legend. During the height of the Galactic Civil War, Boba Fett discovered that the Death Watch sect was still operative, having contracted with Black Sun for addition manpower and secrecy. During this time, their base of operations was hidden in the Red Sin Chimaera Nebula, near the Forest Moon of Endor. The armor of the Death Watchmen was distinctly different from that of the True Mandalorians, although the differences were in color. All Death Watchmen wore stark black armor, and their helmets were modified slightly to further distance themselves from their counterparts. The Death Watchmen were also only group of Mandalorians to regularly wear Mandalorian Crushgaunts, which had been outlawed by the Mandalorian government centuries earlier.

Mandalorian Bloodguard
this was the name given to the primary soldiers of the Death Watch. The Bloodguard were named for their crimson-colored, Mandalorian armor

Mandalorian Death Squad
this was one of the most violent branches of the Mandalorian military, during the years leading up to the Battle of Naboo

True Mandalorians
True Mandalorians - Mandalorian Warriors reunited by Jaster Mereel approximately two decades before the Clone Wars. They followed the supercommando codex which taught them an ethic that extended beyond the limited idealogy of fighting for credits. Existed until around 36 or 35 BBY or so, until revived on two seperate occassions by both Alpha-02 and Shysa and referred to as "Protectors".

The source:
Unofficial Star Wars Encyclopedia
Star Wars Insider #180
Mandalorians Mercenaries

Starwars unofficial encyclopedia