Spell Special Effects
In my OD&D game, spell-casters enjoy the capability to produce minor magical effects related to the spells they have currently memorized. For example, a magic user who has fireball memorized might be able to light his pipe with a small flame from his thumb, or make smoke come from his ears when annoyed. A sorceress with gust of wind memorized might have her hair constantly blowing in an otherwise non-existent breeze. Using a special effect does not cast or use up the spell it is related to; they're not so much "spells" as they are tangible evidence that the magic user has a spell memorized. I do not codify these effects, but rather rely on the players to suggest or request an effect, which I then approve or deny. While I do not have a hard-and-fast rule against special effects that have a mechanical game effect, special effects are always minor, cantrip-like effects.
I like this house-rule for several reasons. First, it adds to the weird otherworldliness of magic users, and I love weird and fantastic elements in my D&D game. Second, it gives low-level magic users something arcane and archetype-supporting to do without using up their memorized spells or abandoning the concept of Vancian magic. Third, it's just cool to play a wizard that can make his eyes glow, or make his smoke rings come out different colors, or whatever. I know that players enjoy the special effects, and also enjoy trying to figure out what spells an NPC caster has based upon what his special effects reveal. The only real danger is allowing effects which are too potent, which could erode the feel of the Vancian magic system. It's up to the referee to make that call on a case-by-case basis.I will definitely be using this rule in any future game I play. Too cool and very playable/logical. No need for cantrips if you interpret the spells a wizard has memorized in this way.