A level 4 Sorceress with Shadow magic is essential.
A Dreadlord with the best possible armour save and Pendant of Kelaeth and Crown of Command on a Pegasus is often advised.
Cauldron of Blood makes a good BSB
Core should be mainly Reapter Crossbowmen, with or without shields, as per your preference.
Black Guard are too good to pass up, I highly recommend always taking 20 of them.
Hydras are ridiculously undercosted, but are so common that most players will build 'anti-hydra countermeasures' into their lists. (well, it's the Hellpit Abomination's fault too...)
Just some quick thoughts. Really though, with Dark Elves, so many of the choices are viable that you can take almost anything you want and it will work out.