Momentum | https://chrome.google.com/webstore/detail/momentum/laookkfkn...

This displays a beautiful photograph on your "New Tab" page instead of a list of your most visited sites, which if you're anything like me is procrastination central. It serves as a reminder for me to slow down, stay focussed, and not obsessively check news, Hacker News, etc... (yep, it's not exactly working at the moment ;-)

It also allows you to specify a main task for the day to keep you focussed but I only occasionally use that.