For Chrome users, an extension to block out those enticing sites that distract you (this is the one I use). if you accidentally try to access a blocked site, you get a message: shouldn't you be working?
"Dark Room is a full screen, distraction free, writing environment. Unlike standard word processors that focus on features, Dark Room is just about you and your text." For Windows.
Another possible Google Reader replacement - has a good rap so far, and promises to work on ANYTHING. You folk with old Safari versions - try to break it.
Great for assembling scrap books of images - settings, moods, characters, inspirations, details, books, authors, booklists, etc. Excellent search engine of collective obsessions. Also addictive.
The history of English word usage. Fascinating for anyone who loves words but essential for anyone trying to vaguely keep things accurate in historical fiction. Also a little addictive.
Free (or very cheap if you want upgrades or cloud version) software for writers, including formatted templates for scripts of all kinds and integrated shooting calendars, production resources, etc