ssh-agent-applet is a Gnome applet that allows you to conveniently keep your ssh key(s) on external media. This means that if your computer is cracked or stolen, the attacker will not have a copy of private ssh key(s).
Using ssh-agent-applet, your keys are loaded into ssh-agent as soon as you insert your "key drive" into a USB port. The drive is automatically unmounted once the key loaded so you can remove it from the USB port immediately.
See INSTALL for details of how to install and configure the applet.