Wizards posted a Prestige Class Index on their site today, covering only official D&D sources.
There are 652 Prestige Classes! Not quite, though, since there are 64 (more or less) classes repeated, so it's more like around 590 official prestige classes. That's a lot of PrCs! Funny thing is, as I look through the list, there's a lot of PrCs that I don't think should bear the name. D&D would be wise to introduce the concept of Advanced Classes, as found in d20 Modern. A PrC should not be something like the Tempest, which basically just turns you into a mobile food processor with two blades, but rather more like the Red Wizard of Thay, Disciple of [Insert Demon Lord Name Here], or Aglarondan Griffonrider, classes tied to prestigious organizations/situations that are demanding but rewarding in both mechanics and roleplaying aspects.
That's what I set out to do when I create/modify a PrC, and that's the reason why a product like Liber Sodalitas: The Blind Path is not just the Unsighted PrC, but rather a whole package of context for the class. I realize a lot of people just use the class by itself, which is why I named that one something rather generic, but it really is very tied to the context I gave it. With Liber Sodalitas: Scions of the Holy Triad I went all out with the concept, to the point where taking the PrC away from the context I gave it actually punishes the class and the character that takes it. It may hurt sales a little (Blind Path sells twice as much as Scions), but as a writer and publisher I need to take a stance. I believe the long-term effects will be much better for me.
Now, what I would really like to see, is that same PrC Index but with as many 3rd-party publisher sources added as possible. Now THAT would be a crapload of classes!