carestad

If your site is depending on posts to have their thumbnail images set, this is the plugin for you. Also makes it possible 
to require tags in every new post.
When trying to save a post without at thumbnail or tags and when activated, the user will get a warning and the post will 
be saved as a draft instead.

Post Requirements

This plugin allows you to require posts to have thumbnail set and/or tags.

Jatinder Pal Singh

This is a simple plugin which is designed to help the posters who some times forget to write the post title. Once activated, this plugin will force the users to give post title while adding new post to wordpress site. Whenever User tries to publish a post without giving title, it will give an alert to the user and also highlight the title area so that user can see where to write the post title.I have tested this plugin with wordpress 3.3.1 and it works fine. It should work with older versions of wordpress also.

Force Post Title

This is simple plugin which forces the users to write POST title in Add New Post page.

Post Requirements vs Force Post Title