Games Workshop is going a bit retro. They've pulled a trio of old Chaos Sorcerer models out of the vaults and are ready to custom-make some when you want to order them. This might be your last chance for a while to pick them up. So get now while the getting is good.
From the website:
Sorcerers of Chaos shape destiny itself with arcane rituals and unspeakable pacts with the malefic entities of the empyrean. They channel the soul-blasting energies of the warp into potent hexes and blasts of wyrdflame, and they mould the fabric of the material universe with little more than a hate-filled curse.
Chaos Sorcerers are powerful HQ choices available to the Chaos Space Marines, Thousand Sons and Death Guard Factions. They are formidable Psykers that can wield the terrible power of the Dark Hereticus psychic discipline (or the Discipline of Change in the case of a Thousand Sons Sorcerer). Chaos Sorcerers from the Death Guard can instead unleash powers from the Contagion discipline.