280 Slides is a notable online replacement for desktop presentation apps. It's fast, functional and very visual.
In it, you can create a presentation, theme it, add graphics and video, and then present it, share it via Slideshare, or download it as a PowerPoint or PDF file. It's so smooth to use that it's hard to tell the difference in the experience between working in a traditional presentation app like Microsoft PowerPoint or Apple Keynote. It doesn't have a traditional app's over-the-top feature set, but it's so fast and easy to use you'll probably not notice that.
280 Slides is in beta, but I was able to create this three-slide presentation as easily as I would in Keynote, and more easily than if I had been using PowerPoint. Cappuccino turned 0.5.5 yesterday. Fellow CNET blogger Matt Asay calls it "exceptional"