I've always been a fan of Bitter Freeze Ray, especially in the absence of an Epic Hold like Char or Dominate. Your build is covering single target, cone, and TAoEs quiet well and based on your slotting, you're going to be hitting +4s of all ranks very consistently thanks to the high Acc in your powers. If you're looking to squeeze more damage from procs out of your build, Ice Blast is the poster child for it - particularly Freeze Ray, Bitter Ice Blast, and Bitter Freeze Ray.