I use this every five minutes or so while I'm browsing.

It works like this: you select a word, hit the assigned hotkey, and a search displays in a right-hand sidebar. I use it with Google, -Images, -define, torrents, iMDb, urbanDictionary, YouTube, and Metacritic. You can navigate the sidebar or click back in the regular page to dismiss the sidebar.

I recommend this to most of my friends. (My parents wouldn't remember all the hotkeys, so they're spared my enthusiasm.) It's invaluable for "Who's that guy again?" kinda searches, and fantastic for finding out if new movies are any good: Image search for the stars, YouTube for the trailer, Metacritic for the ratings, then a torrent site for the film itself. All without leaving my current tab!!!!!1! <<geeking><<

I think there's a version 2 already out, but I'm sticking with this one -- I'm used to the way it works, and I've customized it so much that I don't want to do it over again.