JoVe Apps (www.jo-ve.org) is momently busy with a quiz game for the iPhone(and iPad). But a quiz about which topic? You may say, we listen to you! You can answer in this topic!
One where you don't have to know anything to be right. Oh wait - that's my game! Seriously though, it'd probably be best to "trivial pursuit" it, have a little bit of everything since everyone's taste is vastly different.
A quiz game with a lot of off-beat facts about a variety of subjects (i.e. weird laws, animal behaviours, etc.). I love that kind of thing.