I needed a small screen capture appliction for some documentation that I was doing, because I was tired of having to take the entire screen shot of the whole application, paste into an image editor and crop it down to size... so I decided to write
ScRap.NET: a simple application that allows you to quickly take screen shots of specific areas on your computer screen. Runs in the system tray, and allows you to “draw” the area that you wish to capture. Supports multiple monitors, and copies screen shot directly into your clipboard for easy pasting into any application that supports graphics items in your clipboard.
I know it's nothing terribly original or spectacular, but it works well and serves all of the functionality that I need. It even runs directly from the print screen button on your keyboard, and allows you to still have the full functionality of the print screen button by pressing it twice.