Necrons. Hands down.
The old codex and battlefleet gothic pretty much stated it outright.
The new codex relies more on implication, but if you are looking at the descriptions and manifestations of their technology, the amount of truly bizarre technologies is well beyond that of other races.
Their "sorcerors" function like psykers of other races, but they use raw technological manipulation instead. Gear and abilities such as the Tachyon Arrows, non-warp interdimentional travel, time control, immortality, weather and tectonic manipulaton, inertialess drives, self-aware materials, the Worldengine.