Are there any good resources out there detailing Perlin noise generation? I understand that most languages have noise generating libraries available, but I'm interested in creating my own for fun/experience. I've already looked at this, which seems pretty popular, but it only gives an in-depth explanation of one dimensional noise. Google searches have been relatively unhelpful so far, as most of them focus on applications instead of how to create a generator.

Books and/or websites are welcome, even if their focus is not the generation itself so long as it gives a thorough explanation of an implementation, or at least the concepts involved so I can "discover" my own.