DAs

ing rock!
Feedback owns spell casters. It takes away all of their energy, deals damage to them equal to the amount of energy they had, and costs almost nothing! Take out ther sci ves with feedback and then let your DTs rape his forces.
MC kicks ass in general. It instantly takes away a unit from your opponent and gives it to you. This is great for downing detectors, MCing a spell caster and using it against your enemies in the fray, or just downing a few carriers or BCs.
Maelstrom has got to be my favorite. It stops biological units in their tracks.

ing awesome against muta-ling, or really any zerg assault. It can be deadly if used in conjunction with pisonic(sp?) storm.
The only real downside to them is that they are useless in money maps, but theyre over rated anyway.