Triarch Stalker
A word of warning to this page, if you don't like complicated as fuck models, you will rage.
Triarch Stalkers are giant metal spiders. They are traditionally used for flanking maneuvers and sideswipe attacks, but can do a surprising amount of damage when deployed on the front lines. They can wield a fusion laser cannon that can either be focused into a medium range, melta-style cutting laser, or a wide, fanned out blast of boiling plasma. They also possess advanced targeting relays that can bolster any nearby Necron units' accuracy programming.
The Triarch Stalker is a walker with the Quantum Shielding rule. That means it is AV13/13/11. Neat. Also it carries the Necron's only melta weapon, which it can alt-fire as a heavy flamer. Double neat. Also also it makes every unit that fires on its target twin-linked. WHAT. It can ignore Crew Shaken and Crew Stunned results and it has Move Through Cover. Double neat with chocolate sauce. It makes 3 attacks at S7 in close combat, and only the hidden power-fist (or equivalent) can really scare it. Super neat combo with fries and a drink. Its 150 points for a whole bucket of neat. and you can swap out it's Heavy 2 melta laser for a twin-linked Heavy Gauss Cannon (S9 AP2 36 inch Assault1) or one of the Necron's new guns; the Particle Shredder S7 AP4 24 inch Large Blast).
(While an effective unit, it's another example of "Matt Ward being original", drawing its inspiration from the Geth Colossus of Mass Effect.