Changing the way the date appears in your articles is useful sometimes. The article's date is brought out by string DATE_FORMAT_LC2, so the best way to alter it is change it's value in your language files. Here's how to do it:

1. Access your website files
2. Locate language\en-GB\en-GB.ini (or your own language's .ini file if it is other than English)
3. Change the value of DATE_FORMAT_LC2 to what you wish to see displayed in your articles. 

Examples:

DATE_FORMAT_LC2="d F Y" will be displayed as: 10 December 2011
DATE_FORMAT_LC2="Y-m-d" will be displayed as: 2011-12-10
DATE_FORMAT_LC2="l, d F Y" will be displayed as: Saturday, 10 December 2011

More:

See the date explained in Joomla! Documentation.

See date formatting in PHP.