Greetings!
Hey there S'mon! Yeah, I have developed some serious prestige classes in my campaigns--The Knights of the Wolf, The Knights of the Radiant Dawn, The Knights of the Black Dragon, The Knights of the Shimmering Oak, among others. Most are excellent prestige classes for Paladins and Lawful Good Fighters. I haven't changed the Paladin core class in my campaign, because I'm something of a servant of law, order, and completeness,

so while it isn't like I'm totally incapable of changing it, though it makes me loathe to do so.

I feel more comfortable in making up prestige classes that can fill in the blanks so to speak, so that a 10th level Paladin can take 10 levels in say, Knight of the Wolf, and all along the way, from 11th through 20th level, he can look forward to gaining impressive abilities that suit his actual "role" and "vision" of a holy, mighty, divine champion. I have seen these used with some success, though straight Paladins are also popular, and it isn't like the core Paladin is entirely powerless, per se, because they clearly are not, you know? They do have some power, but if the road gets really rough, some hard-charging Fighters and Barbarians can often times make the Paladin into really a second-string warrior, as you can see problems which the core Paladin presents.
I mean, in some ways, the holy, divine champion, as far as raw *real* power, and braod abilities to actually do many different things and accomplish different challenges, as well as fully inhabit the role of a holy, divine champion, doesn't seem to fully work itself out until the character looks something like this, with a long, epic career worked out:
10th level Fighter/20th level Paladin/10th level Celestial Paragon;
or
10th level Fighter/20th level Paladin;
or
20th level Fighter/20th level Paladin;
or
10th level Fighter/20th level Paladin/10th level Cleric;
as one can see, examining these class combinations against each other, and most tellingly against a straight 30th or 40th level Paladin, the character class's faults and weaknesses are not overcome even with epic levels. The Paladin needs to be supplemented with something else in order to bring it up to a more heroic, mighty ideal. In looking at the various configurations, a straight Paladin seems quite underwhelming, you know? However, it seems that by throwing in a different class or two, like Fighter, Cleric, or Celestial Paragon, the character is able to recoup from most of the Paladin classes failures and actually begin to resemble the mighty vision of a holy champion.
I actually happen to really like the Paladin as a concept, as an ideal, and I even have a passion for the core Paladin class--however, I do think that it is missing the extra bit of rugged toughness and hammering power that the class needs to really live up to the vision and role of the holy champion that the Paladin classically represents.
Semper Fidelis,
SHARK