At Mark’s Hole in the Web, you can check out a neat little toy he made for his blog gutter. It shows a hierarchical list of links in a small space, using animation and interactivity. I really like the colorization — you can see it with two different background colors in the gutter and the content of the blog.
Mark notes that it was quick to write, “weighing in at 120 lines of code.” The links are given using embed/object tag parameters. It would be neat if this read OPML files, and it would probably take even less code.