electric-indent-mode is enough to keep your code nicely aligned when all you do is type. However, once you start shifting blocks around, transposing lines, or slurping and barfing sexps, indentation is bound to go wrong.

aggressive-indent-mode is a minor mode that keeps your code always indented. It reindents after every change, making it more reliable than electric-indent-mode.

• An example of Lisp mode (Emacs Lisp):

• An example of non-Lisp mode (C):

This package is available from Melpa, you may install it by calling

M-x package-install RET aggressive-indent

Then activate it with

(add-hook 'emacs-lisp-mode-hook #'aggressive-indent-mode)
(add-hook 'css-mode-hook #'aggressive-indent-mode)

You can use this hook on any mode you want, aggressive-indent is not exclusive to emacs-lisp code. In fact, if you want to turn it on for every programming mode, you can do something like:

(global-aggressive-indent-mode 1)
(add-to-list 'aggressive-indent-excluded-modes 'html-mode)

If you don't want to install from Melpa, you can download it manually, place it in your load-path along with its dependency cl-lib (which you should already have if your emacs-version is at least 24.3).

Then require it with:

(require 'aggressive-indent)

The variable aggressive-indent-dont-indent-if lets you customize when you don't want indentation to happen. For instance, if you think it's annoying that lines jump around in c++-mode because you haven't typed the ; yet, you could add the following clause:

(add-to-list
 'aggressive-indent-dont-indent-if
 '(and (derived-mode-p 'c++-mode)
       (null (string-match "\\([;{}]\\|\\b\\(if\\|for\\|while\\)\\b\\)"
                           (thing-at-point 'line)))))