SourceKit - A Textmate like lightweight programmer's text editor right inside of Chrome. It saves files directly to Dropbox, so if you have the Dropbox sync software installed, the changes will appear locally as if you did so with a text editor! Changes will be stored remotely so naturally this same extension will pull up the same copy of the file everywhere!
MOG (requires subscription) - As a MOG subscriber, you’ll enjoy unlimited access to over 10 million songs on demand, both on the web and on your TV (with Roku or GoogleTV). Plus, enjoy a revolutionary new radio that reveals the huge limitations of satellite and other Internet radio services. Perfect your music-listening experience: TRY MOG FREE FOR 14 DAYS!
Aviary Suite Extension - Aviary is a suite of powerful creative applications that you can use right in your web browser. We're on a mission to make creation accessible to artists of all genres, from graphic design to audio editing. Let Aviary and Worth1000 artists perform design services for you. Sign up for an account today to start creating, sharing, and collaborating with our community of artists.
These three are awesome for what I'll be using my Chromebook for.