Absorb Magicka/Absorb Magicka (the ones from the ghost weapons in Labyrinthian count as separate enchantments) is pretty ridiculous on a dagger using the Staff of Magnus in the other hand. Burns away their magicka like crazy, switch out the dagger for a shock spell once they're out and they die pretty quick!
Fire Damage + Turn Undead. If you're wearing Ahzidal, or if you have the Illusion perk "Aspect of Terror", you can get Turn Undead effect up to a magnitude of 50 by combining it with Fire Damage, and using the Seeker of Sorcery black book power. This is notable because Dragon Priests are level 50. Throw that on a Silver Greatsword, and add a Flame Cloak or Stendarr's Aura, and you have the ultimate offense against the undead.
I forgot to mention that you also need Augmented Flames 2/2. Possibly the Fire Enchanter perk as well. But if you're going into custom fire enchantments, that probably goes without saying.... Also, I've only tested this with Frost Damage/Fear and Dukaan, using the relevant frost perks, but I see no reason why it would be any different with Fire Damage/Turn Undead. The buff magnitudes are all the same. And it does top out at exactly 50 on the fear effect.
One of my favorite things to do is carry around several sets of gear for different magic schools. If you get the cost down to zero, you can cast really high level spells for no magicka from any school as long as you wear the corresponding gear. Saves a ton on perks too and is great if you want to still use magic after making a magic skill legendary.
For weapons, I love Soul Trap 1 second and Absorb Stamina 1 point. Fiery Soul Trap is all the better. The absorb stamina 1 point means constant power attacks. By dropping the magnitude all the way down you hardly ever have to recharge.
Absorb Health and Stamina destroys warriors.
Absorb and Damage Magicka decimates mages.
Paralyze and Fire Damage will leave them helpless.
Ice and Shock Damage is great for anything.
(This is a personal favorite.) Chaos Damage and Chaos Absorb (You get it from the Dwarven Black Bow of Fate.)