Forget other screen capture programs, right now. ZScreen is advanced and does practically everything you'll ever need in screen capture, and it's freeware and open source.
ZScreen can take a shot of the entire screen, a specific window, or a selection anywhere on the screen, depending on the hot key you press. Then, depending on what settings you had before you started the screenshot, ZScreen will send the image to one of multiple locations.
One very handy feature of ZScreen is the ability to instantly send this screenshot to popular Web image hosting sites Imageshack or Tinypic. If you need to take a screenshot and instantly share it with the world, you can do that--you just have to remember your Imageshack or Tinypic activation code, which ZScreen uses to interface with it.
Alternatively, ZScreen can send the screenshot to an image editor of your choice, upload it to an FTP site, or save it to a file.
There is one thing that ZScreen does not do that other screenshot programs do, and that is the ability to take a screenshot of a scrolling window, and then scroll down during the capture to take the entire image. If you want that functionality, you'll have to use a different program such as Screenshot Captor.
Still, ZScreen is light, customizable and free. Highly recommended.
Note: ZScreen requires Microsoft .NET framework 3.5. If you don't have it, the ZScreen installer can install it for you. ZScreen is donationware. It is free to try, but the author accepts and encourages donations towards further development.