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I don't have a lot of experience with the wraiths, but I hear a Destroyer lord is a popular choice to roll with them. That would be your HQ.

I would probably pick up some swarms as well so you can take advantage of the Spyders spawning ability. You get 3 swarm bases with the Necron warior box set or you can usually pick them up pretty cheap on Ebay if you don't want to have a lot of basic warriors in your army.
Or there are a fair number of alternative models available for swarms. e.g.
http://shop.microartstudio.com/mecano-swarm-base-round-40mm-p-696.html

You might also want to pick up another Spyder at some point because you can have 3 for one heavy slot.

Also get some troops & some shooting to get use out of the Triarch Stalker's re-rolls. Personally I like Immortals.