I really should have focused more on practical matters in yesterday's post about archetypes, so I'm going to do a quick series of posts on each class, starting with the Cleric (because of something Faoladh said that fit with some ideas I had.)
The Cleric is, as I've said, meant to be a representative of the "holy" archetype: a character whose primary motivation is faith, who derives strength from that faith, and is seen to succeed because of that faith. It wasn't exclusively a militant priest, originally. Part of the reason for the Clerics Without Spells article was to allow players more freedom in character conception, so that the Cleric could be used for a traditional missionary, or for Van Helsing, or for Solomon Kane.
The Cleric can be changed further if you recognize that clerical power doesn't (and perhaps shouldn't) necessarily come from a supernatural being, but comes instead from the Cleric's devotion to a supernatural being, or potentially anything else: a megalomaniac, for example, who believes himself to be divine; or a conspiracy theorist, dedicated to revealing the truth. Depending on the setting, these alternative "Clerics" might need other restrictions on or reinterpretations of their abilities, but they provide a little more variety.
Faoladh mentioned the Lover as a possible archetype. There are actually two kinds of "lover": the Don Juan/Cassanova type, able to bed many lovers, and the Lancelot/Romeo type, willing to do anything for their One True Love. The latter can obviously be based on the (spell-less) Cleric, gaining the ability to stare down enemies, persuade the powerful, or even push themselves beyond normal human limits in pursuit of the object of their devotion. Again, they may need restrictions to make them "fit": a Romantic Cleric would not be able to heal others, but might be able to heal himself or dispel fear in order to rejoin his love.
I think the key to adapting the Cleric archetype to non-religious forms is to recognize that the object of their devotion is not really someone or something else, but to some ideal of Loyalty, Fidelity, or Integrity deep in their own character. Replace Piety with one of those three, and subtract a penalty when Very Low results are rolled; Loyalty, Fidelity, or Integrity is slowly restored by selfless acts of devotion (in other words, not expecting a miracle as a result.) For "Clerics" with delusions of divinity, it takes worship or selfless acts by others to restore faith in themselves.