The following two links won't do much if you click them now, but if you drag them to your bookmarks toolbar, clicking the first one there while viewing a Wikipedia page will take you to the corresponding DBpedia page, and clicking the second while viewing the Freebase page for a particular topic will take you to the page full of RDF for that topic.

wp -> dbpedia

freebase rdf

They're both scriptlets, or little bits of Javascript code embedded in links. Each reads the URL of the currently displayed page, does a bit of string manipulation on it, and sends your browser to the resulting URL. I've had the DBpedia one for a while, but I recently found that DBpedia URLs escape parentheses when Wikipedia URLs don't, so I fixed the scriptlet to account for this. While I was at it, I created the Freebase one, which is much simpler.

If anyone's interested, I also have scriptlets to go to a site's home page, an "up" button (cd ..), and a backlink button that searches Google for webpages linking to the currently displayed one.