Many themes developer are loosing aprecious time while creating WordPress themes, because they redefine many CSS style which are already styled by default. In fact, WordPress provide a CSS stylesheet that you can use and save a big time!
If you always wanted to be able to get default styling from WordPress basic elements as such as post images, smileys, the .alignleft, .alignright or .aligncenter css classes you just have to use the wp.css stylesheet.
Just click here to get a preview of what elements, ids and classes this css defines.
To include it on your theme, simply upload the file to your wp-content/themes/yourtheme directory and paste the following line on your header.php file, within the <head> and </head> tags:
<link rel='stylesheet' href='/wp.css' type='text/css' media='all' />
Thanks to Ian Stewart for the tip!