[vram22]

Only a few more keystrokes is:

:sh ENTER

or for more control over which shell, or to run a shell with any arguments, or even to run any command w/ or w/o args:

:!bash

:!bash -o vi

:!bash some_script.sh

:!some_command some args

and after any of those, just press Ctrl-D or type exit ENTER to return to the vim session.

Very fast and easy to do. I use it all the time.