I use Passkeeper for passwords and TiddlyWiki for non-confidential information. Passkeeper is a Windows application, but was portable (no installer required) before portable apps became common. TiddlyWiki is a portable, cross-platform wiki in a self-contained HTML file.
Similar to Carl's setup we use password safe for usernames/passwords, and dokuwiki for everything else. We picked dokuwiki cause it fairly lightweight and doesn't require a database. Because it's all textfile based it's very easy to generate independent redundant copies. When things go wrong you can never have too many copies of your documentation :)
You shouldn't be asking because you should have a solution in place long before you need to ask. Having said that, I use PasswordSafe for passwords, mainly because it is cross-platform. Most other information is stored in a MySQL database, with MS Access as the front on Windows machines.
The company I work for also requires me to provide updated hard copies of all system details and passwords. Those are stored in a fireproof safe at a remote location. They're kind of nervous since the entire building and contents were destroyed by fire about 8 years ago.