Quite a few of the good-aligned and good/neutral classes in the source material aren't such because they're aligned to some cosmic paladinesque ideal, but because they're simply not the thing someone evil would do, or because they imply the patronage of a power who would not bless someone of a black heart.
The defining traits of evil are selfishness and a lack of empathy for the suffering of others. Any class whose core concept revolves around 'doing something because it genuinely helps others', or whose powers 'come from a nonevil patron with goodly intentions', fits perfectly as a good or good-neutral PRC.
A few examples from source material, specifically avoiding anything that is deity specific or is very paladin-esque already:
Branch Dancers - A 5-level ranger-esque PRC, aimed at nature-esque characters. Blessed by a treant, they recieve help from vegetation in the area which literally animates to help them. Requires non-evil alignment, because the treant will not bless those with a black heart.
Church Inquisitor - A 10-level cleric-esque PRC that trades away cleric bonus feats, turn undead synergy, etc, to recieve Detect Evil, a bonus domain (Inquisition) and at 10th level immunity to mind-affecting. Tasked with hunting subtle corruptive evils within outwardly good organizations, only those of the purest heart (LG and NG) are selected for this position, and only after they've proven themselves as zealous hunters of the corrupt.
Daggerspell Mages and Daggerspell Shapers - Respectively, the Arcane and Divine branches of the militant order known as the Daggerspell Guardians. These 10-level PRCs have as central mechanic channeling spells through daggerpoint, combining rogue-esque combat with magical abilities. The Daggerspell Guardians extensively vet prospective members, and will use every mean, magical or otherwise, to ensure only Non-Evil are among their ranks.
Exalted Arcanist - A 5 level PRC available only to spontaneous arcane casters. In a way the celestial counterpart to dragon disciple thematically, this PRC is all about igniting the celestial blood within to gain wondrous new powers via Exalted feats. Offering 4/5 caster level progression and available only to Good-aligned bards and sorcerers, this is a PRC that gains its power entirely from an intimate connection with a celestial power very far back in the character's lineage, like a coualt or planetar.
Prime Underdark Guide - A 10 level rogue-esque PRC that is focused entirely on traversing dangerous locations and obstacles, surviving harsh environments and dealing/negotiating with the various denizens of the underdark. This one is only for non-evil characters, not for any divine or bloodline reason, but simply because this kind of career sounds like suicide to someone who always looks out for number one and has no heart or empathy for helping others.
Sworn Slayer - A fighter-esque 5-level PRC that trades away any kind of bonus feats to instead gain a supercharged version of Preferred Enemy / Studied Enemy that focuses entirely on one single usually-evil creature type (undead, aberration, outsider, etc). There are some divine overtones here, but they're mostly left to the background. None of the classes' powers are actually divine-backed, and are expressed as just highly specialized martial training. Only for the non-evil mundanes of the world that desperately want to rid the Prime Material of these monstrosities.
Vigilante - A 10-level roguebard PRC that combines investigative and social abilities with spells oriented towards sleuthing around in an urban environment, alongside a Smite Evil esque ability usable only against criminals. It's wild and you love it. Again, only open to those who want to dedicate their lives to hunting evildoers.
And finally, if we are going by sourcebook rules,
classes like Knight should probably be non-evil only. From the original PDK, to prestige classes like the Knight Hospitaler, the Anointed Knight, and even in the examples above with the Vigilante and the Prime Underdark Guide, a lot of classes have "nonevil" alignment requirements simply because only decent people would ever pursue them.
There's no need to lock yourselves to 'good equals paladin' when it comes to class design.
Wizards of the Coast certainly didn't.