For a titanium example I recommend Wunderlist. It is used by millions of people on multiple platforms, I use it everyday and it works well. Moreover Wunderlist is a good example for hackers because it is open source: https://github.com/6wunderkinder/wunderlist

main site: http://www.6wunderkinder.com/wunderlist/

One caveat, I'm not sure how many of the current apps (there are 5 versions with an addtional blackberry app in private beta.) still uses Titanium, and Wunderlist has been ported to platforms that are not supported by Titanium. However I know that the first few releases did use Titanium.