280 Slides allows you to create PowerPoint-style presentations online no downloads
Ahead - similar to Prezi in that it is a zooming presentation tool
Bubbleshare - your photos, your voice, your story - narrated slide show online
Capzles is a free web application that allows you to combine your photos, videos, blog posts and mp3s into rich multimedia storylines.
Eduslide - create and deliver your own e-learning
Glogster - create online posters, media rich online posters that can be shared online or embeded onto wikis.
Kizoa - Great site for creating animated slide shows with lots of different content to choose from.
Myplick is a free service that lets you share and embed presentations online. Formats supported are powerpoint, pdf, and openoffice odp.
OneTrueMedia.com produces slide shows from templates with your own photos and music which you can then post online.
PhotoShow - is a nice free site for creating slideshows. All a user has to do is upload their photos from their computer or favorite photo sharing site (a la Flickr, Picasa, etc) and the personalize it and share it w/ others. Also, w/ upgrading to a paid account a user can add video and music.
Prezentit - free online resource for creating and sharing presentations
Prezi is a web application that allows you to create stunning visual presentations. Think PowerPoint meets mind map.
Showbeyond - presentation editor
Shwup - Great site for making collaborative slide shows.
Slideshare allows you to upload and share your PowerPoint presentations. Presentations can then be embedded into blogs or wikis.
Sliderocket - create stunning looking powerpoint style presentations, viewed or shared online
Slideroll - create presentations from stills
Soapbx - create free public presentations online
Thumbstacks - Put your presentations on line to view with any web browser.
Vuvox enables you to create personal, collaborative slideshows or presentations using your own digital media – including video, photos, music and text