How to document my website design? Suggestions please?

I have coded up a reasonably comprehensive website using a variety of MODX plugins. No doubt I am not the only one who has got to this point and then realised that perhaps some design documentation would be a good idea since it's all in my head at the moment ...

Since I have not documented a website design before, I am looking for suggestions as to the best way of going about this.

Any ideas / suggestions?

I generally put HTML comments in important areas and that suffices for our purposes.

I find it convenient to make a text file for each "feature" of the site. For example, if I have an image rotator on the home page, I'll document the TVs, the HTML structure and CSS as well as the Javascript library used for the rotator. I have a folder on my desktop for every site I'm working on, with these files along with other stuff pertinent to that site organized in the folder. I keep it backed up regularly to a USB stick. It gets burned to a CD when I'm finished with the site.

Thanks!