Preezo allows you to create and use presentations directly from their site. Presentations can also be mailed directly to clients. Collaborative working is fully supported. http://preezo.com/

Preezo is an Ajax web application that gives you the power to create and share professional quality presentations over the web without software or plugins.

• Create professional quality presentations using an ultra-fast Ajax user interface.
• Access your presentations from any computer with an Internet connection and a modern browser.
• Reuse images or the content of entire slides from easy to use galleries.
• Save time and reduce headache by collaborating on a centralized web document.
• Distribute presentations to clients and colleages without having to email huge PowerPoint files.

Also see drawanywhere.com

DrawAnywhere is an online diagramming website, where you can draw, modify and share flowcharts and other diagrams, with the look & feel of a desktop application. It runs on any browser with Flash 9 installed.