A HTML5 canvas example: CanvasBalls!
A small example (from when I was learning to use canvas and now tarted up a little) of drawing circles on a canvas. The colours have an alpha channel, for example: rgba(255,0,0,0.5). The dashed canvas border is just some CSS that I've applied to the canvas tag to make it easily identifiable. A far better example of the canvas tag is my canvas based graphing library: RGraph. I was going to add the source code, but as I added animation it grew somewhat. So now you'll simply have to view the source (life is so hard isn't it...?).