Best code documentation resources?

I want to prevent software rot by documenting my code but I'm not sure where to start. I'm finishing up a few projects, one in Cocoa and one in Flash. Before I leave the code to start a new project, I want to document my code so it's easier to get back into in a few months when I update it.

Please share your resources for documenting code? Books, blogs, and podcasts describing the steps to writing clear documentation would be ideal.

Thanks,

David