You can take a screenshot of a specific area, window, your whole screen, or even of a website - apply different effects to it, draw on it to highlight points, and then upload to an image hosting site, all within one window. Shutter is free, open-source, and licensed under GPL v3.
Shutter was formerly known as GScrot.
Aviary lets you snap a screenshot and edit it, all without leaving your web browser view it
With the Aviary Talon add-on you can capture screens from Firefox view it
Windows 7 comes with a Snipping Tool that's easy-to-use! view it
Easy screen capturing and editing with IrfanView view it