Dan Meyer has just launched a new site called 101 Questions on which he is sharing images and videos as prompts for developing math questions. Each image and video has a 140 character field in which you can enter your question. Questions are compiled and can be Tweeted. Take a look at the top 10 to get a feel for what you will find on 101 Questions. I've embedded one of the videos from 101 Questions below.
Incredible Shrinking Dollar from Dan Meyer on Vimeo.
I won't pretend to be able to explain the larger purpose of the site as well as Dan does, so I'll just encourage you to go read his blog post about it. And if you need more background on who Dan Meyer is, watch his TED Talk Math Class Needs a Makeover.