This document aims to give some practical ideas and advice for Internet startups and Internet development shops as to what they should consider documenting when they're writing 'documentation'. There's probably a lot of things on here that you don't need to document in your particular case, and there's probably a lot of things that aren't on here that you do need to document.
Generally speaking, I like to keep written documentation simple. Most documentation should be inline in your code or configuration files… for example, instead of documenting every apache configuration setting you have used, just say somewhere “we use apache; more documentation is in the config file at /etc/httpd.conf ”.
I find it easiest to keep all of this documentation on a wiki accessible to everyone.