Now that Optimizer 1.0 is released, we're heads down working on Optimizer 1.1, scheduled for release at the end of this month. A big part of Optimizer is its reporting and like any visual feature, it is necessary to capture screen shots for marketing materials, user manuals, and bug reports. A good tool to do this kind of thing with is TechSmith's SnagIt. I'm pretty happy with their product and have used it on and off over the last number of years and it works well.
Like all popular products, there are often open source or freeware tools that are comparable. SnagIt is no exception. I ran across a useful screen capture utility other day called MWSnap. With MWSnap I was able to capture screenshots of the entire desktop, a user-defined rectangular area, as well as Windows menus. It also has a few options for drawing borders around the captured image and placing cursors on it, which I've found useful when I was capturing images for user-guides.
MWSnap is not as polished as SnagIt and does not have the comprehensive feature-set that SnagIt does, but for what most people want to do with screen captures, it is awesome. It's small, super easy to use... and free.