I dig Cropper in a big way. It's a great, elegant and lightweight way to do screenshot. However, lately I've been using Kenny Kerr's Windows Clippings 1.0 for posting to my blog.
It goes in the tray and when you double click on it the screen dims. You single click on the window you want to get a screenshot of and just that window brightens. A double-click then will send the screenshot to the clipboard, OneNote, or a Folder. It's even smart enough to pick a good filename based on the Window's Title.
Not only that, but it will create transparency in all the appropriate places, which is very useful when you consider that even Windows Explorer uses irregular regions and curved edges.
Kudos to Kenny for another killer util!