I have seen this link on a forum: http://cb.vu/unixtoolbox.xhtml
It’s called “Unix Toolbox”; a page listing the most used UNIX commands, classified per category: System, Processes, File System, Network, SSH SCP, VPN with SSH, RSYNC, SUDO, Encrypt Files, Encrypt Partitions, SSL Certificates, CVS, SVN, Useful Commands, Install Software, Convert Media, Printing, Databases, Disk Quota, Shells, Scripting and Programming.
As a sysadmin, I find this handy, and it’s a really nice reminder 