While programming(at least in some languages) I often find myself wishing to drag the current line a couple lines up or down. Emacs does have the means to transpose (switch) lines (courtesy of the transpose-lines command bound to C-x C-t), but I find it unwieldy. That’s why I’ve built a couple of custom commands on top of it:

(defun move-line-up ()
  "Move up the current line."
  (interactive)
  (transpose-lines 1)
  (forward-line -2)
  (indent-according-to-mode))

(defun move-line-down ()
  "Move down the current line."
  (interactive)
  (forward-line 1)
  (transpose-lines 1)
  (forward-line -1)
  (indent-according-to-mode))

Those are not the kind of commands you’ll want to invoke with M-x. Therefore I suggest binding them to something like C-S-up and C-S-down(these bindings are often used for the same purpose in other editors and IDEs):

(global-set-key [(control shift up)]  'move-line-up)
(global-set-key [(control shift down)]  'move-line-down)

Since this won’t work on OSX(Control+arrow is used by the window manager) I’d recommend the following alternative to OSX users:

(global-set-key [(meta shift up)]  'move-line-up)
(global-set-key [(meta shift down)]  'move-line-down)

Personally I’m not a fan of any keybindings that require me to move my hands off the home keyboard row, but I wasn’t able to come up with anything better. Suggestions are welcome!

As usual both commands(and both set of keybindings) are available in Prelude(but with prelude- prefices).