If you're looking for design patterns explicity, then you could consider Hibernate a fancy API for implementing the Active Record Pattern:
In software engineering, the active
record pattern is a design pattern
frequently found in software that
stores its data in relational
databases. It was named by Martin
Fowler in his book Patterns of
Enterprise Application Architecture.
The interface to such an object would
include functions such as Insert,
Update, and Delete, plus properties
that correspond more-or-less directly
to the columns in the underlying
database table.
Active record is an approach to
accessing data in a database. A
database table or view is wrapped into
a class; thus an object instance is
tied to a single row in the table.
After creation of an object, a new row
is added to the table upon save. Any
object loaded gets its information
from the database; when an object is
updated, the corresponding row in the
table is also updated. The wrapper
class implements accessor methods or
properties for each column in the
table or view.