Khorne Berzerkers
Berzerkers are Chaos Space Marines with the Mark of Khorne. Lords and Lieutenants, Chosen, Possessed, Chaos Space Marines and Bikers can all bear the Mark of Khorne. Chaos Space Marine squads which are given the Mark of Khorne will become an Elites choice unless the army is led by a model with the same mark in which case they remain a Troops choice.
Errata — Chapter Approved: Codex: Chaos Space Marines Q&A (v3.0): It's theoretically possible under the rules for Khorne Berzerkers to carry bolters — this wasn't deliberately excluded, since some classic Berzerker models are sculpted with bolters, though few players are expected to take advantage of it.
Slaanesh Noise Marines
Noise Marines are Chaos Space Marines with the Mark of Slaanesh. Lords and Lieutenants, Chosen, Possessed, Chaos Space Marines, Bikers and Chaos Havocs can all bear the Mark of Slaanesh. Chaos Space Marine squads which are given the Mark of Slaanesh will become an Elites choice unless the army is led by a model with the same Mark in which case they remain a Troops choice.
Nurgle Plague Marines
Plague Marines are Chaos Space Marines with the Mark of Nurgle. Lords and Lieutenants, Chosen, Possessed, Chaos Space Marines and Chaos Havocs can all bear the Mark of Nurgle. Chaos Space Marine squads which are given the Mark of Nurgle will become an Elites choice unless the army is led by a model with the same Mark in which case they remain a Troops choice.
Thousand Sons
The Thousand Sons Legion of Chaos Space Marines serves Tzeentch and has always included many Sorcerers capable of wielding powerful psychic energies. Since the Heresy many other initiates with a talent for sorcery have turned to Tzeentch but there is one category of warrior that will always be unique to the Legion. In an attempt to arrest fast-spreading mutation within the Legion the Sorcerer Ahriman cast a spell known as the Rubric of Ahriman, which was so potent that every member of the Thousand Sons who was not a Sorcerer was turned to dust and bound forever in his armour as a disembodied spirit.
Thousand Sons fall into two categories, although all bear the Mark of Tzeentch. Lords, Lieutenants, Chosen and Possessed are Sorcerers. Normal Chaos Space Marine squads are instead disembodied spirits trapped within their power armour (although unit Aspiring Champions are still Sorcerers). See the Book of Tzeentch (Gifts of Tzeentch) for more details.
Chaos Space Marine squads which are given the Mark of Tzeentch will become an Elites choice unless the army is led by a model with the same Mark in which case they remain a Troops choice.