It doesn’t actually let you make slideshows online, but you can upload PowerPoint presentations. The real “kicker,” though, is that you can then add audio narration to the sldieshow and post it all online.
As far as I can tell, there are only two other slideshow web tools that also provide this audio option —VoiceThread and Show Beyond. Of course, Flowgram, the top-ranking site in The Best Web 2.0 Applications For Education — 2008, also provides an audio narration feature, but it’s much, much more than a slideshow creator (but can certainly function as one).
I still want to try-out Slide Six a little more, but it’s certainly a candidate to be added to The Best Ways To Create Online Slideshows. I’m also very impressed with its customer service.