Mindmeister lets you create mindmaps online without having to download any software onto your computer. You can share the mindmaps too.
Doodle makes it easy to set up meetings with a bunch of people.
Screencast-o-matic makes it easy to create screencasts - you can add sound, too.
Grazr is one of several sites where you can make your own widgets.
Demo Girl checks out new stuff online and creates demos that you can watch. While scrolling through her blog I discovered Symbaloo which is a very cool way to make your own start page; it's in beta, and it's hqed in Holland, but I love it.