Submission creates an easy to modify form for ‘Blog Carnivals’, ‘Roundups’ or what every you want to call them, basically user submitted content to posts. Original commission and idea by chrisg.com. It has been re-written to be easy to use to none coders, it has been written to allow advanced users to tweak almost all aspects of the look and feel of the form.
This plugin is only supported on PHP 5.2 or greater.
Download and info: http://wordpress.org/extend/plugins/wp-submission/