For the paladin i would like something like crusader strike(wow inspired)
Crusader strike:
A melee strike that deals x%(150% for example) weapon damage as holy damage(or as slay evil)

For priest something like purge, smite etc...(basic damage spells that deal holy damage)

Paladin needs some kind of melee ability other than shield bash IMO.

like the new paladin spell that gives your weapon slay evil (x2 base damage vs evil)?

like the orb of draining spell which does double damage to evil?

Do you mean the blessed weapon spell?
Orb of draining is fine but maybe some hard hitting 3-4x spell with huge mana cost will be useful for nuking hard ones or evil uniques.

Okay but the point is you're really just asking for more sources of holy damage, holy damage already being in the game, merely not referred to as such outside the source code.