OK...thanks for the additional information.
Movies: Do you have a lot of movies purchased via iTunes? Depending on the quality setting (SD or HD) they can take up between 1.5 GB to over 5 GB each. You can safely delete them from iTunes and re-download them again at any time, since they were purchased. If you delete them from iTunes, make sure you confirm to send them to the Trash and empty to recover the disk space.
Other: These can be numerous things - email attachments, downloaded installers, documents, pictures/graphics, iPhone/iPad backups, etc. You can safely delete anything in your Downloads folder if you are sure you no longer need the files. Anything with a .dmg or .zip extension are normally downloaded software installers.
We would be glad to help you determine what is what, but definitely check out the movies in iTunes and the Movies folder as a starting place.
C