dtgreene: Actually, in Morrowind:
* *All* damage spells that you can create are damage over time; you can't create instant spells. You can enchant items with instant spells (just leave the duration of the effect unchanged), but you can't do that with spells.
TentacleMayor: It's been ages since I played it, but if it's like Skyrim then the spells aren't really fire-and-forget but rather channeled. Not quite what I want, or most any machinegun in any game would qualify. TES also punishes using heavy armor when casting spells and while there are defensive spells, they compete for magicka with destruction spells. So bleh.
Skyrim is actually diffgerent from previous games in the series when it comes to magic. In earlier games in the series, you just cast a spell once, and it has its effect, which can be a damage over time effect. So, you could create a long-lasting damage over time spell, cast it once on the enemy, and then just hide or run away until the spell wears off or the enemy dies.
The only TES game I am aware of that penalizes you for wearing heavy armor (or light armor, for that matter) while casting spells is Oblivion; I know that Daggerfall and Morrowind have no penalties at all for wearing armor and casting spells. (In Arena, casting spells in heavy armor is impossible because there is no class that can equip plate mail and cast spells; on the other hand, a powerful custim Shield spell does not wear off with time, and you can just rest after casting it to get your spell points back, but unfortunately the Continuous damage effect is broken in that game.)
Also, Morrowind and Oblivion allow you to place custom "Cast when Strikes" effects in your weapon. So, you could equip your magic weapon, hit an enemy, then run away or switch to another weapon while the enemy is taking damage; in Oblivion, armor won't interfere with this. Also, if looking at Oblivion, don't forget that you can use Alchemy to make custom poisons, which can do really nice damage if you're patient.