As CptMetal said, Transports! Definetly pick up a venom or two (obviously with twin splinter cannons), but also a raider if you decide to run Kabalites in larger squads.
And as for the wyches, make at least one into a Succubus to save yourself havin to buy a seperate HQ.
"Whereas the duty of the Imperial Commander is either to seize or defend territory, the Dark Eldar make war only to steal. If, as a by-product of this, the are able to indulge their vile passion for murder, torture and other decadent acts, then they will joyfully do so, but this is not their primary goal"