Google has come out with the full release version of Google Desktop 2
. It has a great desktop search capability which beats the pants off of Windows, but I like it for the sidebar. Email, news, weather, and all sorts of other things at my fingertips.
I've been playing with writing plugins in Visual Basic.Net, and with the help of some great people at Google, I have a version of a sample plugin that is very close to working. In the meantime, they decided to add scripting as another option for making plugins. It's more limited than using COM, but there still are a wide array of possibilities for plugins.
Of course, there are already quite a few sidebar plugins available. Check it out, more great freeware!