A teacher in our week-long Teaching and Learning in the 21st century summer institute asked if there was a list of "widgets" that could be used in a blog or wiki.
I googled "widgets for blogs" and came across Widgetbox. On their page they have a link to widgets that have been tagged for "education." Some really interesting content: Grammar Girl, a scientific calculator... hundreds or thousands. Some are obviously more educational than others, but there's some good stuff here if you're willing to spend some time browsing.