There are quite a few good bare-bones introductions to Dojo widgets out there, but not a lot beyond the Hello World stuff. Here is a bit, as I find it and figure some of it out...

The recent 0.3 release added an amazingly convenient method for creating new widgets, dojo.widget.defineWidget, which I'll use for all my widget making -- it is just that much nicer =)

 dojo.widget.defineWidget("skife.sample.CommentPane", dojo.widget.HtmlWidget, {
  templatePath: "http://morphy.skife.org/src/dojo-samples/CommentPane.html",
  templateCssPath: "http://morphy.skife.org/src/dojo-samples/CommentPane.css"
}) 

For more information…

Dojo, Widgets