This is a great site if you live in the US, but not so great if you live any where else. Basically this site lists the locations of some of the surviving gems of the video game world, where you can find them and play them. Granted it does have some locations for the UK and around the world but not as extensive as the US listings. Trawled through the net to see if theres anything more comprehensive like this for us poor sods in Blighty, but no joy yet. Let me know if you find anything.
UPDATE 2023: Classic Arcade Games Locator – Used to be located at: arcadelocations.classicgaming.gamespy.com, but this is long defunct. A more modern locator one can find and it covers everywhere around the globe (albeit still focused on the US) is Aurcade.com.