Ionic Spark + Deathblade. Thank me later.

The theory behind this is that nearly every champion uses abilities that trigger Ionic Spark, which upon that champion's death will give the equipped champion a stack of Deathblade, giving them an additional 15 AD each time it triggers. This can be especially useful for comps with high attack speed like Rangers or Wilds, or simultaneous attacks/attacks in quick succession like Gunslingers or Blademasters.