Shell echo-sed quine:
echo sed -eh -es/[\\\(\\\\\\\\\\\)\\\&\\\|]/\\\\\\\\\\\&/g -es/^/echo\\ / -es/$/\\\|/ -eG| sed -eh -es/[\(\\\\\)\&\|]/\\\\\&/g -es/^/echo\ / -es/$/\|/ -eG
echo sed -eh -es/[\\\(\\\\\\\\\\\)\\\&\\\|]/\\\\\\\\\\\&/g -es/^/echo\\ / -es/$/\\\|/ -eG|
sed -eh -es/[\(\\\\\)\&\|]/\\\\\&/g -es/^/echo\ / -es/$/\|/ -eG
I wanted to write a sed quine, but sed can only work on its input stream, not generate output spontaneously, so this is an echo-sed quine. This 154-character quine uses command-line sed, which automatically makes it hard to read, and uses three different sed commands, as well as two sequences of eleven backslashes in a row. This quine works in bash, ksh, and sh, but not csh or tcsh.
EDIT:
A blatant, and amusing, cheat: echo $BASH_COMMAND
Another, unreasonably silly, cheat: export PROMPT_COMMAND='echo $BASH_COMMAND';$PROMPT_COMMAND