Using ScreenShot2Email is one of the quickest ways I've found to send screenshots by e-mail. All that you need is to define hotkeys on your keyboard (such as Print Screen) and the program automatically makes a screenshot for you at the touch of a button. It even saves it in the pre-configured format of your choice no matter what the original image format.
ScreenShot2Email has a user-friendly and very simple interface. It also allows you to perform some post production actions such as add comments or watermarks. Having hotkeys definitely makes taking screenshots easier although this program features far less features than programs like SnagIt. However, I like the fact that it compresses the image to the smallest size possible automatically so that sending it by e-mail is easy.