Technically speaking neither the Word Bearers nor the Iron Warriors have one (Dark Apostle and War(p)smith were originally exclusive to the two, but they are now just thematic/characteristic of them and technically generic), but the corresponding classes still have a strong aesthetic/conceptual association with them. The Black Legion also formally does not, but Veteran of the Long War is as Black Legion as you get (you get to pick an Alignment if you want one and then pick a piece of equipment and special ability from any other Space Marine class of your choice that shares that alignment or lack thereof, which is thematically pretty representative of the Black Legion). Thus, in terms of having a suitably themed/characteristic advanced class, every Legion can be said to be accounted for, and given that Veteran of the Long War covers the generic non-specific CSM/Black Legion advanced type and Tome of Decay also covers the quite general areas of Possessed, Black Crusades, and Daemon Princes (i.e. high level Black Crusade RPG) I have a hard time believing we'll get another expansion sourcebook.
I mean there are technically renegade Chapters like the Red Corsairs left, but that's about it. I guess also the Fallen of the Dark Angels, I rather dislike the Heresy novels and have no idea what their current status is (whether they are actually supposed to be Chaos Space Marines or not) in the most recent backstory. I feel like there isn't much territory left to cover as far as distinctive Chaos Space Marine advanced archetypes go, however.
Edited by Andkat