[Tools] Cropper the C# Screen Capture Program
It doesn't really matter what language the tool is written in, but this program happens to be one of the smoothest screen capture utilities around, and it happens to be written in C#. I've been using it for months, and I have no plans to replace if for another cropper/clipper/capture tool.
It's available on CodePlex and there's also a Cropper Plugins project there with a bunch of more or less useful plugins :)
(picture from the Cropper CodePlex site)