Noctur.nl is a Google Maps based database of cafes, restaurants and bars that are open late (past 9pm). Currently there are over 36,000 places in the database and the site is growing all the time.
Users can submit their own favourite late-night haunts to the map. The site uses Twitter for authentication and for reviews. On each individual establishment page there is a Twitter textarea where users can tweet from the location and let people know what they thought about it using a short description and a simple rating system.
Major cities in the USA each have their own Google Map. Map markers in the shape of Owls with their eyes open indicate places that are currently open, owls with eyes closed and Z's above their head indicate places that are closed.
Nocturn.nl also has mobile support and support for iPhone geolocation. The site is currently US only but there are plans to expand coverage throughout the world.