AndNav2 is Android's first
turn-by-turn navigation app, marking one of the first instances where Android's wide-open apps policy has put it at an advantage over the iPhone. At least, in Europe. UPDATED 10:38 EST
Since the software is based on the OpenStreetMap mapping data, the app will be more useful in some areas than others, as the map information is, at least in part, crowdsourced like Wikipedia. The app itself, though, is polished. The search and directions functions will be familiar to anyone who has used a satnav unit (or even Google Maps) before, and the turn-by-turn functionality seems solid.
The main issue with AndNav2 is availability, as their site lists versions for Germany, France, Denmark, the United Kingdom, Spain, Switzerland, Italy, Austria and Ireland, but not the US. This could be an exclusion based on insufficient mapping data for the country, but in any case there's no reason that you couldn't install the British version and at least try it. The alpha release of AndNav2 is available here.
UPDATE: Nicolas Gramlich, the man behind AndNav, got in touch to let us know why there's no US version: logistics. Opening the app to running routes through North America would require a much larger server than the one they're using right now, for which the developers are trying to secure donations (you know, from you). And honestly, the app is free, so settle down, quit yer whinin', etc. [AndNav via MobilitySite]