Developing a site with WordPress I needed to delete the Category base from the URL.
By default WordPress adds category to the categories.
I was Googling arround and I found two solutions.
A. Code Solution
Add this line to your .htaccess file (in your root WordPress installation folder)
B. Plugin Solution
You can use this plugin wich does not require any kind of coding or set up.
WP No Category Base
The plugin requires no setup or modifying core wordpress files and will not break any links. It will also take care of redirecting your old category links to the new ones.
Download it from: http://wordpress.org/extend/plugins/wp-no-category-base/