Robin Good: ProShow Web is a free web app which allows you to upload your preferred images and video clips to create fancy-looking video slideshows.

The free service provides hundreds of music tracks that can be used without additional cost to score your visual creation.

You can customize the slideshow visually by utilizing one of the many ready-made templates already available, and by selecting the order of images and clips, adding transitions, effects and text information.

The final video (which remains always "editable" in your account) can be easily uploaded to YouTube, shared on Facebook or downoaded in your preferred format and video resolution.

A "Pro" version is available that provides more features and higher quality outputs. 

More info: 

(via Baiba Svenca)