Google Maps Navigation, forgetting that our friends in the UK don't have the same luxury. Leave it to Electricpig to connect worlds, finding a somewhat hack-induced way to bring the app upgrade to British Android 1.6 devices. Instructions are pretty easy, so if you're game, don your DIY hat and click over.
Update: As indicated, the gang at xda-developers forum have been doing this for some time now. Consider the tutorial provided here as very straightforward and easy to follow -- anyone with an Android 1.6 device would be remiss not to give Navigation a shot now.