There are lots of ways to kill a non-responsive Linux application from the terminal. If you'd rather just click a button or two to kick malfunctioning programs to the curb, you can add a "Force Quit" option to your desktop panels.
At the How-To Geek's main home away from Lifehacker, Linux geek Trevor points out a tool you can add to the top or bottom panels in Ubuntu — but, presumably, in other GNOME-based Linux desktops as well. The "Force Quit" button does mostly the same thing as a killall x command, but you'll get a crosshair pointer to pinpoint the app that's not responding. Click it and that app should shut down. It obviously won't fly with non-graphical applications, but for most apps on a personal installation, Force Quit can make for a nice aggravation-saver.
A full step-by-step guide, with screenshots, is available at the full How-To Geek post.