Online code beautifier and formatter

CSS: code beautifier

HTML: HTML Tidy, CleanUp HTML or the general purpose Pretty Diff

Javascript: http://jsbeautifier.org/

PHP: http://beta.phpformatter.com/

SQL: http://dpriver.com/pp/sqlformat.htm

XML: http://chris.photobooks.com/xml/default.htm

Colour all: http://quickhighlighter.com/

For PHP, Java, C++, C, Perl, JavaScript, CSS you can try:

http://www.prettyprinter.de/index.php

You can use Perl::Tidy for Perl.

JsonLint is good for validating and formatting JSON.

What language?? There are different tools for almost every imaginable programming language, since they all have different syntactic rules and conventions.

Good ol' indent is a nice, customizable, command-line utility to format C and C++ programs.

It depends of the language, and of the architecture you are using.

For example, in a php platform, you can format almost language with GeSHi

As bluish comments, GeSHi is a generic syntax highlighter, with no beautification feature. It is more used on the server side, and combine it with a beautification tool can be tricky, as illustrated with this GeSHi drupal ticket.

I've used Quick Highlighter a lot. Works great for a huge list of languages.

Use gist.github.com. There is a multi-language support(java, c, c++, c#, vb, haskell, ruby, javascript, lua, HTML, SQL, Tcl, Perl, JSON, groovy...)

Here is a sample "Generate LiquiBase changeLogs using Groovy"