I just got Fantasy Flight Game's new rpg, the Black Crusade, today and immediately read the parts about Dark Eldar. Most of it was pretty standard and familiar to aybody who has read the codex, but there were some interesting tidbits. The book includes rules for Kabalite warriors, Mandrakes, Incubi and Cackling Abominations (this is a new unit, and a very interesting oen at that), aswell as Harlequins and Shadowseers representing non-Dark Eldar.
Warriors: Nothing particularly interesting here. Most warriors are armed with splinter rifles, which use antigrave technology to fire poisoned crystal shards at extremely high speed, but for boarding actions and close quarter combat they may isntead use splinter pistols and monoblades. Entry also mentions dark lances (which it describes as firing streams of volatile dark matter) and disintegrators (which hurl large globs of impure dark matter to clear massed infantry). No rules for those, atleats not under the warrior profile (haven't read through the entire weapon section so they migth be there). The disintegrator thing might be an error and they meant the blaster, altough the description seems to match the old plasma cannon-esque disintegrator.
Mandrakes: Pretty much the same stuff as in the codex. Mandrakes move in an unnatural way and people looking at the find them extremely unsettling. If a Mandrake has killed somebody within the last 24 hours, it may use the balefire attack.
Incubi: No rules for the tormentors, sadly, altough the klaivex has the option of taking demiklaives and a bloodstone. Incubi are used as bodyguards as they are only loyal to their own caste and have no interest in political advancement. Unlike other Dark Eldar, the Incubi don't care about inflicting pain and suffering, only about killing as much as possible and as efficiently as possible. They do not, however respect or revere the ideal of martial expertice, it is merely the means for the end (the end being killing things).
Cackling Abominations: This is a new entry to Dark Eldar forces, and is quite interesting, It is, for all intents and purposes, a Dark Eldar-made Daemonhost. The first of these things was created long ago when a truly mad Haemonculus, whose name has been long lost to history, was seeking to better understand the connection between his people and Slaanesh captured a Daemonette for study. To his frustation, he found that Daemons, not being made of flesh and blood and posessing minds incomprehensible to mortals, don't respond veyr well to torture. To solve the proble, the Haemonculus used arcane magic to bind the daemon's soul into the body of an Eldar slave, the subjected the newly created Daemonhost to experiments so bizarre they defy descriptions. In the end the daemon was driven quite insane and perpetually trapped within the twisted body it had been bound to. The creture looks like a distorted and stretched Eldar, with long arms ending with razor-sharp talons. It's face is permanently contorted into a wicked grin and it's mere presence spreads madness around it. It creeps around silently to catch it's prey by suprise, then tortures them to death while cackling madly.