Creately - Online Diagramming and Design is a fully interactive web-based application that runs in your browser. Designed with ease of use in mind, the Creately application consist of 2 screens, namely the Document Manager and Diagram Editor.
The Document Manager displays all your diagrams in Projects with Tags. You can easily organize and manage your projects, diagrams, tags and sharing permissions from this screen.
New Project - Manage your Diagrams in Creately's Team Projects
Organize your Diagrams with Tags
Open a Diagram from the Document Manager
Share your Team Projects with your Collaborators

The Diagram Editor is divided into 4 sections. This deliberate design lets beginners get on with their tasks without the application getting in their way, with all the power hidden away until you really need it.
Creately's Object Library - Simply drag and drop shapes from the library onto the Drawing Canvas.
Drawing Canvas - With multiple tabs so you can open as many diagrams as you need.
Right Panel - For Data & Smarts, Comments, Sharing, Help & other advanced features

Comments
Add pages to document?
Really great product.
RE: Add pages to document?
You can't add pages to documents or diagrams but you can easily link diagrams together and organise them in Projects with Tags.