Jing is a great tool for adding basic visual elements to all of your online conversations.

Gyazo is an open source screenshot program for Windows, Mac OS X and Linux.

Grabilla is a software that takes a screenshot of the user's computer screen and uploads it to the Web, FTP, computer or copy to clipboard.

Screenshot Captor is a tool for grabbing, manipulating, annotating, and sharing screenshots.

Shotty is a screenshot utility.