In classic Dungeons & Dragons, magic is "Vancian" regardless of the spellcaster's class. Magic-users memorize mystical formulae and clerics pray for them (coincidentally for the same length of time), but spells always boil down to words that are charged with energy from the Positive or Negative Material Plane, which, when activated, are promptly erased from the spellcaster's memory. To be regained, the magic-user must memorize them again and the cleric must pray for them again. I recall reading somewhere that the magically charged words of a spell (or verbal components if you prefer) are impossible to understand or remember for anyone who happens to hear a spellcaster utter them. These words are more than words. They are the essence of primordial power. Not even another spellcaster can recall the words of a spell by hearing them. They must be committed to memory by a period of study lasting no less than one hour (in Basic/Expert D&D) or 15 minutes per level per spell (in AD&D).
This is all well and good and I have no problem with any of it as it applies to magic-users, but there's something a little wonky as it applies to clerics. I have no problem with clerics sharing the same limitation of a certain number of spells per level, nor with clerics having to pray to regain spells, but I do have a problem with the words. That is, I do not like the verbal components of clerical spells to be identical in nature to magical spells, i.e. impossible to understand; impossible to remember. Clerics, as priests, are in the business of communication. They study the message of their faith, whether it involves interpreting scripture, interpreting omens, or speaking with spirits. They disseminate the message by preaching to congregations or spreading their faith as missionaries. Clerics communicate. Now, certain religions may indulge in a fair amount of obfuscation for various reasons (such as the use of secret symbolism to protect them from persecution if they are oppressed, or the use of complicated rituals and hierarchical structures to maintain power), but one thing most religions are not shy about is communication. It therefore stands to reason that the "spells" for which a cleric prays are not the arcane formulae memorized by magic-users, destined to fade from memory within seconds, unable to be understood even for a second by the uninitiated. On the contrary, clerical spells are words of power that manifest divine will through the agency of the cleric, and those words are a message that can be understood by anyone.* As the power to cast a spell is granted by a cleric's deity (or, in some cases, the deity's divine servants), the essence of the spell is not a formula to be understood by the cleric, but a message to be conveyed by the cleric.
I would go so far as to say that any player character wishing to cast a spell as a cleric must state what his or her character is saying in order to make the spell work. This needn't be a formally composed invocation, but rather a statement of the cleric's faith and a supplication to his or her deity to enact the desired effects of the spell. This works best if it is stated in character in the player's own words. The same words are not required whenever the same spell is cast. In fact, it probably serves the game better if the words are personalized to reflect a given subject, situation, or location. The words chosen would certainly vary dramatically depending on the cleric's patron deity or sect. Each spell that is cast becomes both an affirmation and an act of proselytization (and it makes playing clerics more enjoyable, too).
I should add that the words themselves, in a clerical spell of this type, do not trigger a spell's effects. It is the cleric's entreaty, the cleric's expression of desired intent, that enables him or her to become the vessel of divine will. The words alone do nothing if they are not accompanied by the cleric's faith and piety.
I think this makes clerical spellcasting significantly different in flavor (and more interesting) without the fuss of new mechanical rules.
* Even in a game world with multiple spoken languages, I think I would rule that the clerical spell as uttered would be miraculously comprehensible to anyone regardless of their familiarity with the cleric's language.