I knew most of these but the $_ variable and "ESC + ." to reference or insert the last argument of the previous command. I can see getting some use out of that, so thanks for posting.

or - as an alternative to <esc> + ".":

for the last argument

* <alt> + "."

if you want the -<n>th argument:

* <alt> + "_" # n times :=)

* <alt> + "."

cheers a..z