I recently encountered this list of terminal tips and tricks (for Mac OS X, but most are more generic) and, as often happens, learned something new: with the bash shell, the command C-x C-e opens the current command line for editing in the editor defined by the $EDITOR environment variable. However, this doesn’t work for me out of the box in my preferred shell, zsh. Zsh does have a capable multi-line command editor built in, so the utility of the above is somewhat diminished. Even so, it would be handy, and it turns out not to be difficult to enable. Just add the following to your zshrc:

autoload -U edit-command-line
zle -N edit-command-line
bindkey '\C-x\C-e' edit-command-line