Have a look at clojuredocs.org. I think it's one of the best documentation sites I've seen for any language or library. I especially like the inclusion of source code and links to other code that uses the thing being documented.
An example: http://clojuredocs.org/clojure_core/clojure.core/condp
I concur. That site's documentation is the best I have ever seen. The documentation on the main page is pretty good too:
Re:Why PHP Was a Ghetto
by InclinedPlane on Wednesday April 20, 2011 @03:39AM
(#2465673)
C#, Java, and other languages have abundant online documentation as well. What's more, their documentation isn't filled with the vagueness and ambiguity that plagues PHP's documentation.
http://php.net/arrays
http://php.net/extract
http://php.net/oop
I hardly memorize stuff 'cause it's so easy to look up to the docs that it's not necessary. And here is what you get when you don't really know what you are looking for:
http://php.net/array_implode
That is just nice documentation...