There are several publications about patterns in j2me:
Architectural manifesto: The MVC design pattern in MIDP development by Mikko Kontio
Identification of Design Patterns for Mobile Services with J2ME by J. Narsoo and N. Mohamudally
Big designs for small devices by By Ben Hui
Patterns I use sometimes:
MVC - to separate UI from controller classes and data structures, may be useful for code reuse on different platforms
Command - to reuse code in user interaction and app work-flow
Interface - to simplify several components use (ex different types of connections or data storage) and component testing (see Blackberry - change latitude and longitude on the device to test app)
Also Observer may be used for UI update tasks(see sample with HttpRequest)
What are your favorite patterns in J2ME/BlackBerry?