The ever-clever Scrap Princess has posted about mixing up the core four classes with each other- so the fighter learns spell-like fighting moves, while the wizard buys the halbard spell.
I really like her ideas about the cleric using the thief's percentage skill system to perform a limited set of magical tasks, spell-like abilities, and such. I also like it because it finally puts the cleric as a character class that is "skill" oriented like the thief more than the fighters "weapon" orientation and wizard's "magic" orientation.
This, in my mind, makes a good symmetry: The fighting-man uses physical weapons to defeat the opponents while the magic-user employs arcane weapons. The thief uses their skills to manipulate the physical realm for their betterment, while the cleric uses their skills to manipulate the spiritual realm for the greater betterment (of their god).
She lists the follows as short list of classic cleric abilities:
-banishing supernatural agents
-trapping said agents if they can tricked or convinced to enter a vessel
-casting out possession
-healing sickness, infertility, curses
-fertility (land /domestic animals/ people)
-weather prediction-dispelling illusions/detecting of supernatural influence
-protective wards against disaster or ill intend-assessing auspiciousness of dates , partnerships or signs-omens
-lay dead to rest/ placating angered ghost or spirit
Of course, converting the thief abilities into spiritual ones could be fun:
Hide in shadows (of your god's glory): gain AC bonus (Lawful), attack bonus (Chaotic) or skill bonus (Neutral) as your god manifests through you
Move silently (and avoid the dead & fate): escape the notice of the dead or a failed saving throw (if you fail to, suffer twice the fate)
Find & Remove Traps (of the soul): remove curses, geas, alignment changes, & lycanthropy
Hear Noise (of the gods' whispers): with the appropriate sacrifice, you may attempt to prognosticate
Climb Sheer Surfaces (out of the grave): percentage chance you will arise provide your body is not eaten or desecrated
Open lock(ed hearts): Recruit folks to your cause provided they are of like alignment or neutral
Pick pockets (of those who should donate to your god): Gain funding from the common man for your pious quest from street preaching