This procedural medieveal fantasy city generator by Oleg Dolya is really something else. While it may not create city layouts that are the most functional, it always creates something that is nice to look at. When I found this on Twitter I spent a lot of time tweaking the parameters and generating city after city.
Stuff like this makes me wish I finally got off my ass and built my dream iPad app, the "Dungeon Master's Best Friend". I'm a huge fan of pen-and-paper role-playing games but I don't believe we should try to completely digitize them. There is something about sitting around a table with your friends while rolling dice and using a pencil and paper to keep track of things. We lose the soul of the game the more we try to replace it with computers. However, there are many facets of the game that a Dungeon Master has to contend with which would benefit from being supplemented by a computer.
For example, what to do when a session goes off the rails because your players set off in a direction you weren't anticipating? Being able to take five minutes to generate a city (or maybe even just a crossroads or a forest encampment) that is populated with some NPCs and an encounter or two would be extremely useful. Doing this doesn't replace the need for a Dungeon Master. It simply allows them to focus on the kind of creativity and character and world building that a computer simply can't do.