Are there any databases or indexes of Web Services?

I'm looking for something that categorizes the various services and then either (1) documents how to use them or (2) links to the documentation so I can learn more.

From stackoverflow

• You may like ProgrammableWeb Mashup Matrix, under APIs section.

• There is no comprehensive list of all web services in the world, if that's what you're asking. That makes sense when you think of how many web services there must be in the world, both public and not-so-public.

  When you say "so I can learn more", what is it you want to learn? Even if there were such a list, I'm not sure what you could learn from it that you couldn't learn better elsewhere.