This is a move-line function (by Joe Smith) that was discussed on the gnu-help mailing list back in 2008. This function allows the current line to be transposed up and down. This is useful for re-arranging lists in Emacs.

See MoveRegion if you want to move the entire region. See also the move-lines package for moving indifferently current line or lines surrounding region.

(defun move-line (n)
  "Move the current line up or down by N lines."
  (interactive "p")
  (setq col (current-column))
  (beginning-of-line) (setq start (point))
  (end-of-line) (forward-char) (setq end (point))
  (let ((line-text (delete-and-extract-region start end)))
    (forward-line n)
    (insert line-text)
    ;; restore point to original column in moved line
    (forward-line -1)
    (forward-char col)))

(defun move-line-up (n)
  "Move the current line up by N lines."
  (interactive "p")
  (move-line (if (null n) -1 (- n))))

(defun move-line-down (n)
  "Move the current line down by N lines."
  (interactive "p")
  (move-line (if (null n) 1 n)))

(global-set-key (kbd "M-<up>") 'move-line-up)
(global-set-key (kbd "M-<down>") 'move-line-down)

See also standard command ‘transpose-lines’, bound to ‘C-x C-t’. – DrewAdams

DrewAdams suggestion of ‘transpose-lines’ works like a charm. It makes the implementation of M-up and M-down trivial. – ThomasKappler

(defun move-line-up ()
  (transpose-lines 1)
  (forward-line -2))

(defun move-line-down ()
  (forward-line 1)
  (transpose-lines 1)
  (forward-line -1))