Wraiths can be ery usefull as well! Especially vs warriors! Be sure to use them vs their warriors armed with two handed weapons or additional handweapon since that will make the wraiths S5 most effetive! Get them under the influence of VDM and they'll smash those warriors up good!
Watch out for marauder harsemen with mark of khorne since they will hit much harder than they look capable of! Especially if armed with flails! Altough, a small dire wolf unit will easilly(spelling?) redirect those pesky pony riders away from the main battle due to their frenzy.
I would also watch out for rear charging them with zombies! Sure you'll negate their ranks and get +2 for rear charge BUT those zombies wont even sratch the metal of those warriors anbd the rear rank of warriors will turn those zombies int minced meat in seconds! The mot efective use of zombies vs WoC is to raise a small uit behind him when you have engaged him in close combat. Then just let them stand their 1" behind to catch them if they flee. Also, most warrior units only come in 12 strong so negating their ranks and getting a rear charge will only give you a +3 advantage, but I can assure you that that rear rank will smash up about 7-8 zombs givinh you opponent a +4-5 advantage instead wich can be VERY devastating agains your other undead unit in the same combat since all of your units must crumble if you loose. So, zombies an very well bring down your entire army rather than helping out.
Also, remember that chaos knights make magical attacks so don't try to bogg them down with etherals.
Thats all for now, hope I've helped!