iPhone: Annotable is one of the best image annotation tools around, especially after Evernote abandoned Skitch a couple of years ago. Now, it's been updated with a slew of new features, making it much more versatile.
Tagged With annotation
Mac OS X Leopard only: One of the built-in Mac utilities that got the most feature additions in Leopard—albeit pretty quietly—is Preview, the PDF and image viewer. We've already covered how you can do more with Preview in Leopard, but Mac OS X Hints points out another good one: image annotation. Add arrows and notes, or circle and outline areas of an image in Preview using the Annotation menu. (In Preview's View menu choose Customise Toolbar, then drag the Annotate menu onto the toolbar.) Then, when you're editing a non-PDF image in Preview, just select your annotation, and click and drag on the image itself. Handy, and no third-party software required. Annotate non-PDF images in 10.5's Preview
Add interactive comments to your YouTube videos with the new annotation feature. To annotate to any video you've uploaded, just head to your uploaded videos page and click the Edit annotations button. From there you can add comment boxes, speech bubbles, and even links to other content. The catch during the beta test is that annotated video only appears on videos playing directly on YouTube and not embedded on other sites, but you can get an idea of the possibilities by checking out this annotated video. YouTube isn't the first to introduce this sort of functionality, but you can bet you'll see a lot more annotated video now that they have. YouTube Video Annotations
Webapp the Awesome Highlighter aims to give context to shared links by allowing users to highlight text in a webpage before they send it out. Very similar to previously mentioned web site Jump Knowledge, the Awesome Highlighter creates a special URL that saves your highlighting schemes and displays them when you click through to the link. It's good to give quick context to a link, but if you want to heavier annotation, Jump Knowledge is a lot more feature-rich.