Burden in Oblivion. Awesome for locking enemies where they stand. Open Lock in Oblivion too, awesome spell for Mage, making him really jack of all trades.
And I love Absorb Skills and Attributes spell from Oblivion right now thanks to my Connoisseur. I´m curentlly messing around with Drain spells there.
Also, Reflect Spell and Reflect damage in Oblivion is awesome.
Well, I guess you can say that I like all Oblivion spells.
Right now playing with the Requiem overhaul for Skyrim, which changes the names of spells and introduces some Oblivion spells back into the mix. This is great because undead, including vampires are a nightmare.
Sunfire and Sunburst (Sunfire and Vampire's Bane in Vanilla). Love nuking them undead and then making them run away.
Animate lockpick in Requiem is one of those Oblivion spells that have been brought back. Love it.