As I had difficulties to organize my own collection of links about widgets of interest to educators, I set up my own gallery:
widgets for education
(a widget is a very small piece of software doing *something*)
As this was started more than a year ago, I have a pretty good overview of the desktop widgets (the ones that live on your personal computer). But over the last months, there has been a total explosion of web widgets and I don't have them well covered.
If you are kind enough to add a comment with information about widgets that you have on your own blog or that you use in the context of your teaching activities, I will add them to the gallery (mass updates are easier -- they will take place at least once a week).