Triarch Stalker
A word of warning to this page, if you don't like complicated as fuck models, you will rage. But atleast this one is less croissant-shaped than other Necron models.
Triarch Stalkers are giant Necron 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. Their advanced targeting relays can bolster any nearby Necron units' accuracy programming.
The Triarch Stalker is a walker that ignores Crew Stunned/Shaken, has Move Through Cover, and possesses Quantum Shielding, giving it AV 13/13/11 until the first penetrating hit, all for 125 points. It carries the only Necron melta weapon, which it can alt-fire as a heavy flamer (making it one of the the only Necron weapon able pierce through the bullshit 3+/2+ cover every point-scoring unit have nowadays), and grants all allied units around it +1BS, for that extra dollop of "fuck you." It makes 3 attacks at S7 in close combat, and only the hidden power-fist (or equivalent) can really scare it. You can swap out it's Heavy 2 melta laser for a twin-linked Heavy Gauss Cannon (S9 AP2 36" Assault 1) or the Particle Shredder (See: heavy psycannon) (S7 AP4 24" Large Blast). They can deploy in a squad of one to three, and form the linchpin of an excellent Decurion formation.
While an effective unit, it's another example of "GW originality"; it's pretty much the love-child of the alien tripods from H.G wells War of the Worlds and the Geth Colossus of Mass Effect (seriously, calling it's main gun a a Heat ray? not even trying G.W).