I remember about two years ago, before a trip across the Atlantic, trying to find websites that had street maps for London and Dublin – and coming up nearly empty.
Now, a year after it became available, I notice that Google Maps covers Ireland and the UK. Unfortunately, it does a piss-poor job of finding locations: try typing anything more specific than Dublin into the search box.
Google Maps now provides a basic ability to get directions between cities.
Some other map links: