`IMO, !$ is most useful of them all (it is the one that gets replaced with the last argument of the last command).`

I've been liking Esc+. for this. It doesn't usually work in browser sessions though, have to do Ctrl+[+. which is a strange feeling 3 finger salute. For some reason I'm able to remember that one rather than !$

Edit: apparently Alt+. does the same, wow.