A very simple and useful stopwatch
$ time read (ctrl-d to stop)

List of commands you use most often
$ history | awk '{a[$2]++}END{for(i in a){print a[i] " " i}}' | sort -rn | head

Reboot machine when everything is hanging
$ <alt> + <print screen/sys rq> + <R> - <S> - <E> - <I> - <U> - <B>

Create a script of the last executed command
$ echo "!!" > foo.sh

Sharing file through http 80 port
$ nc -v -l 80 < file.ext

save command output to image
$ ifconfig | convert label:@- ip.png

Graphical tree of sub-directories
$ ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/ /' -e 's/-/|/'