As it relates to the actual casting of spells, I prefer if the caster makes some kind of check related to her skill at using magic to cast her spells and to determine how potent or effective the spells are.
Darn, completely forgot about those sorts of variants.
That's alright. There are so many possible options that you'd really have to run a thread like this just to get input as to the poll choices if you wanted a truly thorough poll.
One example of what I'm talking about would be the magic rules in the Cinematic Unisystem games (i.e. the Army of Darkness, BtVS, and Angel rpgs). You roll a skill check (1d10 + magic stat + magic skill) and the umber of success levels you get determines how powerful a spell you can cast (it works sort of like spell level, only the level is the minimum number of success levels you need to cast the spell), and how powerful the effects will be. In the case of damaging spells, the damage is usually success levels x magic stat x some variable determined by how powerful the spell is.
Another example would be the
incantation rules for D20 Modern, which are sort of similar to 3e's Epic handbook's
epic spell rules.
BESM d20 also had a system that used fatigue points and replaced spell levels with DCs to cast. If a character could take the appropriate amount of fatigue and could make the skill check, the character didn't need to be concerned with the spell's "spell level" anymore.
I also liked the skill checks to cast the 4e rituals, but I think they really could have expounded upon that with rare special components that could kick the skill check, multiple casters, and other things.
I also recall a 3e 3pp book that had feats that let you substitute things like costly components or additional casting time for the increase in spell slot level required by casting a spell with the effects of metamagic feats.