Windows/Mac/Linux (with Adobe Air): TweetDeck—most popular Twitter client among Lifehacker readers—just released an update to version 0.33, bringing with it more support for viewing media inline without opening a page in your browser (including YouTube videos and Flickr images) and a nice new column navigation tool. Sound good?
Windows/Mac/Linux (AIR): Say what you will about newspapers, but the old gray ladies are laid out for quick reading. Cross-platform app (and webapp) Readefine breaks any site or feed into column-split articles and easy access jumps to other posts.
Windows/Mac (Adobe AIR): Desktop widget application Snippage displays snipped portions of web pages as widgets on your desktop, so you can keep your eye on your to-do list, email, or anything you'd like.
Windows/Mac/Linux (with Adobe AIR): Note-taking application Scribbly lives in your system tray and lets you quickly write notes or reminders to yourself, and then will email them to you with a single click.