Chrome/Chromium: If you're running a daily build or development version of Chrome that can install extensions, online editing suite Aviary has a really handy one. It takes snapshots of web pages and transports them to its online editing tools.
Aviary's online image editor, Phoenix, is a favourite of Lifehacker readers, and their other tools, like the Myna audio editor, are none too shabby, either. Aviary's Chrome extension makes it easy to push that image to its markup, image, colour, effects, or vector editor, and there's a link to Myna included for good measure. Once the image is in Aviary's editor, it's easy to download it, broadcast it to Twitter or Facebook, or perform any of the other tasks Aviary's apps offer.
The Aviary extension is a free download, and should install wherever Chrome extensions can—generally, that means daily builds on Mac and Linux systems, and the Dev version on Windows.