My new favorite way to play necrons is robot horde. These little guys in large numbers is not a force to be taken lightly. I have been running just big units of 20 necron warriors each containg a base necron lord with resurrection orb and then ghost arks filled with 10 more warriors. Since the Resurrection orb gives your guys a 50% chance to reanimate and then the Ghost arc has a potential to rebuild up to 3 warriors per turn you can lose half of your unit and almost bring everyone you lost back to life. This usually leaves your opponent frustrated. Since gauze weapons auto glance on a 6 an unit of 20 warriors with gause flayers can handle just about anything. The downsides to this list is all your weapons have a 24in range therefore an army with lots of long range shooting can be trouble sum if your trying to get close enough. Also necrons are terrible in close combat you want to avoid getting assaulted by scary close combat units.