Here are the some of the popular mobile apps in some of the top trends. Most of the apps listed out here are available in all popular mobile platforms like iPhone, Android etc.

1) Maps, Navigation, Location based search
http://www.sygic.com/
http://www.tomtom.com/en_au/products/mobile-navigation/
http://www.loopt.com/
http://foursquare.com/


2)  Social Networking
www.facebook.com
zephyr
Twitter


3) Mobile Payment
http://mashable.com/2010/01/01/mobile-credit-card-readers/


4) Mobile Advertising/Marketing
http://mashable.com/2010/04/08/apple-iads/
http://www.althosbooks.com/intomoad.html – This briefs about Mobile Advertising architecture
http://www.admob.com/


5) Mobile Search
http://www.taptu.com/corp/