- Higher level casters are rare.
- Body must be relatively intact; completely missing body parts are not regenerated, and certain missing body parts (head, brain, heart) prevent raising. No raising skeletons!
- No Con loss; a failed adversity roll means body is too damaged to be raised (but steps can be taken to change this and try again.)
- The omission of halflings is an oversight (all standard races are raise-able.)
Father Dave's comment talked about using Raise Dead in the context of a very Christian version of Clerics. I am not a Christian myself, but paradoxically, I prefer a somewhat Christianized version of Clerics when I'm running or playing in a pseudo-medieval setting.
These days, I'm thinking of Clerics as Devotees of the Light; they are at least nominally monotheist, but not necessarily the same religion, although all are united as servants of Law. Neutral Clerics who aren't druids are more concerned about their specific religion -- Christianity, Judaism, Islam, Zoroastrianism, Mithraism, Manicheanism, or some fictional stand-in -- than about a united attack on the forces of Chaos. They are thus part of the same church as like-minded Clerics of Law, but Lawful Clerics are able to recognize other Lawful Clerics of other religions as being "on the same side", even if they disagree over particulars.
Chaotic Clerics are anti-clerics (heretics.) They are opposed to all the religions and philosophies of Law, but (being Chaotic) not necessarily united with each other. They are in it for themselves, making bargains with lower powers or serving the powerful out of fear.
In small, secret pockets of society or outside of the civilized areas, there are pagan cults. Clerics of these cults do not have the Turn Undead ability, but might have a different ability in its place; they might have the same spell list, or they might have a modified or completely unique spell list.
That's all pretty trivial, but what I was actually thinking of, as I read Father Dave's comment and his blog post about St. Cuthbert, is that in addition to Lawful Clerics possibly being of different religions, they could be devoted to different saints. Since I'm more devoted to generating backstory during play, my idea of saints is a little different. I figure a shrine or chapel dedicated to a specific saint passes a single spell to the priest of that shrine, even if that priest is not technically a Cleric. Each saint might actually have a themed set of spells that "defines" that saint, but each shrine gets only one spell, based on the comparative "level" of the shrine. A little out-of-the-way shrine to one saint might grant a first level spell, while the most important shrine to that saint might grant a fifth level spell.
So, although I would make high-level NPCs (including Clerics) rare, there would be an option in my world to find someone able to cast Raise Dead: travel to the most important shrine of the saint known for raising the dead. Adventurers must first ask around to find out which shrine is rumored to grant that miracle. They must then travel to that shrine, and talk to the priest there to see if he will do so. There may be a quest involved, possibly magically-enforced. And even then, it may turn out that the priest isn't actually faithful to the saint of the shrine. The adventurers might have to find one of the faithful to become the new priest.
None of this is strictly just to make Raise Dead more difficult. It's to make interesting stuff happen. Going to the nearest temple, plonking down money, and getting someone resurrected in a ho-hum way is not very interesting; making Raise Dead rare and encouraging adventure to find it is interesting.