This is one of those questions that will raise a thousand different answers
My answer is: It depends on what your project is!
sandard ones I tend to use are
* util (For any utility classes, some people like to have one big util package, others have util packages at various levels)
* persistence (for the data access layer and other persistence)
* domain (for 'business' domain objects)
* security (for any security specific classes)
* plugins (self-explanatory)
* management (for any management interfaces/code I might build)
At the end of the day how you cut and slice it will be dependent on what you're building. You'll also often find that you'll want to restructure your packages later on, a good refactoring tool makes this fairly trivial.