Simple One to One using assigned identifiers (meaning you hae to set the id yourself) http://www.xylax.net/hibernate/onetoone.html
Using Formula’s in hibernate mappings and some other neat tricks round computed fields http://www.onjava.com/lpt/a/6092
Hibernates Own Reference Documentation
http://www.hibernate.org/hib_docs/v3/reference/en/html_single/#mapping-declaration-onetoone
… Chapter 7 on associations gives some examples. http://www.hibernate.org/hib_docs/reference/en/html/associations.html