I'll mention it here, because I learned about it here.

"~C" will drop you into the SSH command line, allowing you to, among other things, effect port forwarding

  -L8080:localhost:443

Learning that "~C" exists, and what you can do with it, has supercharged my use of SSH tunnels, which were already awesome on their own.

But for some reason this has been disabled by default in more recent ssh configurations... to ensure its available

  -o EnableEscapeCommandline=yes

or, in your ~/.ssh/config

  EnableEscapeCommandline yes

(edit: formatting)