47:  How do I show which parenthesis matches the one I'm looking at?

  Emacs 19 comes with paren.el, which (when loaded) will automatically
  highlight matching parentheses whenever point (i.e., the cursor) is
  located over one.  To load paren automatically, include the line

    (require 'paren)

  in your .emacs file.

  Alternatives to paren include:

  * If you're looking at a right parenthesis (or brace or bracket) you can
    delete it and reinsert it.  Emacs will blink the cursor on the matching
    parenthesis.

  * M-C-f (forward-sexp) and M-C-b (backward-sexp) will skip over one set
    of balanced parentheses, so you can see which parentheses match.  (You
    can train it to skip over balanced brackets and braces at the same time
    by modifying the syntax table.)

  * Here is some Emacs Lisp that will make the % key show the matching
    parenthesis, like in vi.  In addition, if the cursor isn't over a
    parenthesis, it simply inserts a % like normal.

      ;; By an unknown contributor

      (global-set-key "%" 'match-paren)

      (defun match-paren (arg)
        "Go to the matching parenthesis if on parenthesis otherwise insert %."
        (interactive "p")
        (cond ((looking-at "\\s\(") (forward-list 1) (backward-char 1))
              ((looking-at "\\s\)") (forward-char 1) (backward-list 1))
              (t (self-insert-command (or arg 1)))))