I've been using Windows Movie Maker to make slideshows with musical backdrops. The two problems are (A) the maximum output resolution is 640x480 and (B) it only exports in the WMV encoding. I would like to find new software that allows me to specify whatever bitrate / resolution and encode in h264. A Google search returned hundreds of results, so I'm asking the community which slideshow maker they've had best experience with.
Haven't used it myself, but DVDslideshowGUI might be what you're looking for.
It's an interface for Avisynth (amongst others) and also supports direct encoding (as per the homepage):
PS: Have gone for free / open-source programmes