Desktop environments like KDE and GNOME make it possible for you to assign keyboard shortcuts to a number of global operations, but don’t make it easy to create shortcuts to run any program you’d like. To set up shortcuts for programs, XBindKeys is the way to go. XBindKeys, as the name implies, binds keys to a command. It runs in the background and waits for you to run a shortcut that’s defined in its configuration file. It handles virtually any key press (not just the modifier keys that your window manager recognizes) and is easy to set up.
for ubuntu-users: xbindkeys is available in the universe repository;
sudo apt-get install xbindkeys xbindkeys-config