This should be quick as there is just two options!
Chaos Space Marines: Try no to compare them to a Grey Hunter, they won't match up once you pay the 2 points for the extra close combat weapon, still another point and you can take +1 leaderhip and hatred. Then add a mark and some weapon options to me becomes stronger and more flexabile unit for the game. Oddly GW seems to discourage MSU with this unit build making it more worthwhile to invest in larger squads.
Chaos Cultists: Got Cultists? Take them! for 135 points I can pack in 35 cultists, take a character and they are fearless. Not as great as they used to be but oh what the hell! Cheap squads now for Chaos!