ePubPress

From the page:

EpubPress is a browser extension for Chrome & Firefox for turning your favorite web content into ebooks.

Benefits: 1)Removes ads and other distractions, for a cleaner reading experience. 2) Makes content available offline, for reading on the go. 3) Viewable on all your devices (Kindle, Nooks, iPhone, iPad, PC etc.). 4) Groups relevant content together.