If you use a custom bit.ly account for shortening urls and then tracking clicks across things like twitter, facebook, emails, blogs, etc., then you’ll surely find the bit.ly plugin for Windows Live Writer useful.
LiveUpload to Facebook 2.0 was just released. If you use Facebook, then this is a must have Windows Live Photo Gallery plug in. You can get it from http://www.codeplex.com/liveuploadfacebook.
The Windows Live Photo & Video blog keeps a list of known plugins here: