Optimal renders valid OPML from any source in a tree-like view ideal for browsing. Links to external OPML files as well as RSS, RDF, and Atom feeds are expanded in place.Optimal can be installed as a WordPress plugin -- it is the successor to my OPML Renderer for WordPress plugin.
MashLogic: Take Back the Web (By Getting Awesome Links) It's like a frickin' Swiss Army Knife for hyperlinks, I'm putting this on my must-have list of Firefox addons.