Once I got my magic resist up to an ungodly level dragon priests were a joke. Heh I had antronach and lord stone running for a while and that was just goofy easy. Swapped to my aetheric crown to ritual just so I could have a badass army every now and again. Deathlords were scarier, and only if they decided to melee. (Seriously - bethesda next time make it so that fire/frost/magic resists cap out before it's make magic damage a non-issue!)

The stupid Master Steam Golem. That Steam attack does SO MUCH DAMAGE.
Also, Frost Dragons kick my warrior's butt

Fun Fact: this doesn't affect melee warriors. If you just run straight to them, the steam literally goes over your head.

Any Ice Storm mage, particularly the one at the end of the Break of Dawn. Damn him.