As Zaphod Beeblebrox and vinnyT state, a KVM switch works a treat.
I'm using a Belkin 2-Port KVM switch - mainly to use mouse and keyboard. My flat screen (a Dell) has both anologue and DV interfaces, so I don't need the KVM switch for monitor sharing. Both work fine in different modes, but need to adjust the screen when changing. (press one button)