Doing some research on HTML5/Canvas usage I found theses tools on the web:

• Pencil Project: graphic editor, nice replacement for dia
• Web Sequence Diagrams: simple and useful UML sequence diagrams tool, I also like the Human Drawing editor from the same author, nice code.
• Typeface , Cufon, StrokeText: 3 libraries used to add embeded font support on a page (and for other js usage).
• demos there, I especially like the '3D walker'
• http://code.google.com/p/iecanvas/, http://code.google.com/p/explorercanvas/ some libs to try adding canvas support in IE