Cropper is a great .NET screen capture utility, created by Brian Scott, that allows you to capture any part of the screen via a re-sizable window. Output can be redirected to BMP, JPG, PNG, Printer and Clipboard.
Output is created by simply moving and resizing the Cropper window to the area you want to capture and then double-clicking or pressing Enter with the Cropper window selected.
An example of Cropper in use from Brian's Blog:
Cropper can be downloaded here.