I think the biggest Win spell of them all is Force Field.  
  
I use it all the time to disable yellow/orange marked boss enemies, then clear out the mooks (I haven't come across anything yet that managed to resist it). It lasts for around half a minute, which is an eternity. It's also useful to send a tank into a horde, let the tank Taunt, then cast Force Field on the tank and unleash some arcane mayhem.