Red Hat 5.9 in here, and it looks amazing i hear. Go here for a excellent read about it:http://securityblog.redhat.com/2013/01/16/enterprise-linux-5-8-to-5-9-risk-report/
Read all about the fixes and updates included in the releases and see how up-to-date RedHat keeps your systems. And do not forget that RHEL 5.9 will keep getting updates until March 31st 2017. Read on.
Check out for the Next RedHat training near you, if you are in Portugal read on: http://formacao.rumos.pt/seccao2.rumos?id=8