Rapidfire Cannon + Elise
I found this combination pretty interesting.
The attack speed helps Elise gather mana quickly so she can shapeshift and the range makes her fairly easy to protect like an Ashe, Varus, or Trist.
Once she shapeshifts, the spiderlings serve as a front line and she is able to continue to attack from a range.
Her lifesteal in spiderform works very well with the extra attack speed as well.
One thing though, which may be a bug. I am pretty sure once she shapeshifts, she has 3 range instead of 2. I would imagine this is because the bonus range from Rapidfire Cannon is calculated while she is in ranged form, doubling her 2 to a 4 range. When she shapeshifts, instead recalculating her range so that it is 2 instead of 1, it only drops her base range and keeps her bonus. I'm not 100% positive that this is CURRENTLY the case, but I am pretty sure that this is what I saw when I tried this. I imagine this is more of a calculation oversight than a bug, but I will probably create another post in the bug category just to be sure.