Highway Route Markers collects highway signs from around the world. The Upstate New York Roads Site lists (and reproduces) every exit sign for many of the state's freeways. Let me reiterate: Every. Exit. Sign. The net has something for everyone, even those of us with an unhealthy obsession with road signs.
Ireland's road signs are notorious for getting travellers lost, but the Irish government has announced that it will finally do something about it.