Drawing an arc with javascript

Depending on what platforms you want to support and the complexity of the drawing, I would suggest either DHTML , canvas (with ExplorerCanvas for IE).

Although DHTML is cross-browser, canvas seems to be suitable for future projects as it is capable of so much more and is actually intended for use in graphics.

Edit: Either I was wrong when I originally wrote this, or ExplorerCanvas was actually using flash to render its canvas. but now they seem to have switched to VML and / or Silverlight. I edited my answer to exclude this dependency. I've also added a stronger canvas suggestion.