Google Blogoscoped reports Google has released Google Presentations as part of Google Docs.
This provides a way to build a presentation online, with a system familiar to anyone who uses Powerpoint. Due to the application being web-based, the presentations can be easily shared, allowing collaboration in building the presentation. Of course there is also a way to publish and share the presentation online once it is complete.
Perhaps don’t rush to share it just yet - they also report a security flaw which introduces Privacy Problems Introduced Google Through Presentations. Check the comments on that post to see when the issue is resolved.