Once again, Microsoft shows that it's the best when it comes to WYSIWYG word processing. Windows Live Writer is a blogging application that can detect your blog's CSS (i.e. to get the layout your blog uses for your posts). You could therefore see exactly how your post will look like while you're writing it. Here's what it looks like. For geeks, there's an HTML Code mode so you could fix some very minor markup quirks that the beta seems to have (like putting random s into the code).
Writer is compatible with major blogging services like Microsoft's own Spaces (of course), Blogger, LiveJournal, WordPress, etc. In fact, I'm using it right now. There's a problem posting images for Blogger, but that's the Blogger Team's fault for not implementing image uploads in their API.
Oh, here's the direct download link to the installer.