Thumbs Up for Hyperwords
Hyperwords is an extension for Firefox and Flock that I've really been digging recently.
It allows you to select any text & choose a command from the resulting pop-up menu: search, look up references, blog, email, copy, translate and more. Basically, it makes every word on the web interactive.
Here's a quick demo video.
You can download the extension here.
Try it out!