command-completion for C- commands?

[knubee]

Tabbing works to show possible completions of Meta commands. Example:

M-x list-f<TAB> shows

  Possible completions are:
  list-faces-display               list-fontsets

Is there an equivalent way to see possible completions for Control
commands -- given the mode of the current buffer? Example:

C-x<WHAT?>

thanks.