Are you using a wiki format? If so, which product? (MediaWiki, Confluence, Sharepoint etc.)
Have you create a knowledge base? (Problem/solution-oriented short documents.)
What challenges do you find with creating documentation that works, so you don't get the call when you're off on holiday?
For me, I find there is often a certain amount of organisational "inertia" involved with getting documentation done. It seems to be a different kind of person who can do a task, then think about how they did the task and describe it so someone else can do it - kind of forces to you "go meta" and not everyone is comfortable doing that.
Answers so far include
- Mediawiki (with plugins such as fckeditor)
- Word/Excel/Visio Docs
- Documented Scripts
Edit: Aren't you implicitly documenting your network with your monitoring system? Nagios has always encouraged the use of the parents directive to reflect your network's structure, and the notes_url directive is designed to allow you to link to a wiki or other browser-based documentation. So here the "documentation" is split between the "living document" of the monitoring system and more detailed, offline documentation in a wiki. Since I spend a lot of time staring at Nagios it makes sense to put effort into making it as informative as possible.