I'm a big fan of Vista Sidebar gadgets -- and I like the Sidebar-less Windows 7 gadgets even more. My major complaint? There just aren't enough good gadgets available. That's okay; Amnesty Generator makes thousands of existing widgets compatible with Windows.
Amnesty Generator is free and easy to use. You don't even need to know where to find widgets on your own; the program itself includes a directory of common sources such as Google, the New York Times, WidgetBox, and dozens more. When you see one you want, just copy the HTML from the gadget page into Amnesty Generator and the program does the rest, depositing a fully functional gadget in your Windows Gadgets collection.
How much you might like Amnesty Generator depends entirely upon whether you use the Windows Vista Sidebar. Personally, I love this free little app: It's given me a seemingly limitless library of gadgets, and access to desktop conveniences that were tantalizingly out of reach with Vista's gadget library alone.