One of the most useful information that the Oracle kernel attaches to plans in the library cache are measures of various resource consumption figures, such as elapsed time, consistent and current gets, disk reads, etcetera. These can be made available for each plan line (aka "row source operation").
These figures are always cumulative, that is, include both the resource consumed by the line itself and all of its progeny. It is very often extremely useful to exclude the progeny from the measure, to get what we could name the "self" figure (following, of course, the terminology introduced by Cary Millsap and Jeff Holt in their famous book Optimizing Oracle Performance).
As a minor but useful new feature, xplan is now able to integrate into its report the DDL of tables (and indexes) referenced by the plan, calling dbms_metadata.get_ddl transparently.
This is mostly useful to get more details about referenced tables' constraints and partitions definition - to complement their CBO-related statistics that xplan reports about.
This feature can be activated by specifing dbms_metadata=y or dbms_metadata=all (check xplan.sql header of xplan.sql for more informations).
We spoke about xplan in general here.