Awesome Screenshot for Google Chrome does annotations, sharing
What makes it awesome? For starters, it can capture both the visible portion of a page or the entire thing -- and scrolling web pages aren't always support by capture tools. It's also got a nice built-in editor which provides all the functions I typically need when cleaning up a screenshot: crop, shape drawing tools, arrows, editable(!) text, and a blur tool for hiding sensitive information.
When you're finished editing, your image is presented on the page and you can save it locally via a right click or upload and share with the push of a button.
Here's my one gripe about the extension: the links it provides are gigantic. Like many tools which upload to pict.com, the URLs Awesome Screenshot spits out are way longer than, say, an imgur or yfrog link. That creates an extra step sometimes if you're pasting a link into apps which don't auto-truncate.
Hopefully future versions will offer a choice of image host -- if so, Awesome Screenshot will be even better than it already is. And it's already pretty dang good.