Yup, withoutabox.com
It is how I have submitted films for student projects I have helped produce. The application form is a bit long but it guides you through it. Just make sure you are prepared with multiple copies of the film on DVD in case the fests come calling.
Also, keep in mind that many of the fests require a submission fee. I reccomend going through the site and making sure you do it all correct. Also, only submit to fests that your film fits into. (IE - male filmmakers shouldnt send submissions in to fests for women filmmakers...)
Good luck!