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)