Google has completed their free online suite of office tools with the launch of Presentations. Like Docs and Spreadsheets, Presentations can be used to create and store PowerPoint compatible files. Fully integrated with Docs and Spreadsheets, it is a viable alternative to Microsoft Office. I intend to introduce my students to presentations because of the ability to collaborate. Now students who need to work together to create a presentation do not need to be in the same location. By sharing the file with one or more collaborators, every member of the group can work on the presentation and the teacher can see what contribution each member made to the project.
I encourage you to give Google Docs, Spreadsheets and Presentations a try. Get started by going to Google Docs and selecting the "new" button. Select "Presentation" and you are on your way.