Snagit, by TechSmith, is a robust screen capture program that allows you to capture part or all of your screen in a snapshot or a video. You can then use the editor to add text, stamps, and other annotations. It is available for both Windows and Mac. The full price is about $50, there are volume and educational discounts. It really is my favorite and I use it every day.
If you are on a tight budget, this may be too much, or you may not use it enough to justify the cost. If you want a simpler program that is free, consider Jing, by TechSmith. It works much the same as Snagit, but without the editor. You can still capture a screenshot or video and either save the file or store it in the cloud via ScreenCast.com. It is available for both Windows and Mac.
If you like Jing, you'll also like TinyTake. It, too, is a free screen capture and video recording Windows application. TinyTake also includes annotations and share them online.
Another free alternative close to Snagit that allows annotations, is GreenShot. It's a free and open source Windows application that is easy to install and use. You can create screenshots of a selected region, window or full-screen. The screenshot can be saved to file, send to printer, copied to the clipboard, and more.
I am quite impressed by PicPick, which is not only a screen capture application, it is also an image editor. Adobe Photoshop is a great, but a complex and pricey tool. PicPick is a simple image editor that allows you to adjust brightness, contrast and color, grayscale, blur, pixelate and other special effects. Don't forget, it is also a screen capture tool. You can capture your full screen, active window, user-defined area and more. PicPick has a selection of other tools that I currently use other programs for, such as pick a specific color on your screen (I use Instant Eyedropper), magnify something, or use a virtual whiteboard to "draw" on your screen (I use Zoomit for both of these).
If you do need a little more and have a small budget, consider Snap, by Ashampoo. For just under $20 you get a Windows screen capture application with shots and video. Plenty of options for annotations exist and you can save in common formats or upload to Facebook and Twitter or the Ashampoo webspace. It is very similar to Snagit with a better price. A big plus for Snap over the others is that it is touch-optimized for your touch screen devices.
These are only a few of the many, many options out there for screen capture. Check these out and comment on your favorite in the comment section of this blog post.