Katla is a user generated content theme for WordPress made by Bluthemes. It offers the ability for users to submit content to your website via a custom made form. All the submitted posts are inserted as pending posts so a moderator can review the submission and do any changes if necessary. This is very similar to websites like 9gag.com and boredpanda.com, now you can easily make your own!
Demo: http://themeforest.net/item/katla-user-generated-content-theme/11143562