Surprisingly, there aren't a huge number of screenshot tools for Linux. Luckily, they don't need to be, because the feature-rich Shutter is about as awesome a program as you can ask for.
If you're not familiar with screenshots, read our beginner's guide.
- Take screenshots of your entire screen, the active window, a region, and even a web site
- Customizable hotkeys let you snap screenshots in just a few keystrokes
- Tons of built-in options for choosing the default format, compression level, directory, and more of an image
- Built-in editor with annotation features like text, arrows, and shapes
- Share to the web through an FTP server, Ubuntu One, or external services like ImageShack Flickr (via another program)
Shutter is feature-filled without being difficult to use. It's designed extremely well, offering an easy way to take screenshots of the entire screen, a region of the screen, a specific window, or even a web site with the click of a button. You can annotate and crop it with its built-in editor, and share it to a few external services. The options menu is chock full of tweaks you can make to get it working exactly how you want, if you're so inclined. In short, it's the most powerful screenshot tool on Linux, and even rivals similar tools on Windows and Mac.
Shutter is pretty awesome. My only beef with it is that it doesn't support a lot of external services. Flickr integration is available through another program, but beyond that and ImageShack, you don't have a lot of choices if you want to share your pictures. It could probably have a few more hotkeys, too, but its wealth of options still makes it the most powerful program around.
Linux doesn't really have any other screenshot tools of this caliber available. A new app called Lookit is currently in beta, which brings some nice features to Ubuntu Unity and the GNOME 3 Shell, like right-clicking on the dock icon to take a screenshot, or support for Unity's notifications. It isn't quite as powerful, but Ubuntu users might like it.
Other than that, the default screenshot tools for GNOME and KDE are both pretty solid if you're looking for something basic. They're both quick and provide all the simple options you might want, like adding a delay to your screenshots, including the cursor, and so on. If Shutter is overkill, they should be more than good enough.
Know of a screenshot tool we didn't mention? Let us know about it in the comments. The screenshot world seems pretty bare on Linux these days, and we're eager to find more.
Lifehacker's App Directory is a new and growing directory of recommendations for the best applications and tools in a number of given categories.
Windows: We've covered a lot of screenshot apps in the past. If you use Dropbox for most of your working documents it may make a lot of sense to use CloudShot, the screenshot app that automatically uploads to a specified folder on your system, including Dropbox folders. 
Mac/Android: Skitch, one of our most popular screen capture tools, was bought today by the company that makes popular note-taking tool Evernote. What does that mean for us? The full version is now free (down from $19.95) and there's a new Android app. 
