How to find out the version of CentOS?

[root@rubyplus ~]# uname -a
Linux rubyplus.tempdomain.com 2.6.18-53.1.6.el5.028stab053.6PAE #1 SMP Mon Feb 11 20:53:20 MSK 2008 i686 i686 i386 GNU/Linux

Doesnt tell much

[root@rubyplus ~]# rpm -qa | grep centos
filesystem-2.4.0-1.el5.centos
basesystem-8.0-5.1.1.el5.centos
procmail-3.22-17.1.el5.centos
initscripts-8.45.14.EL-1.el5.centos.1
httpd-2.2.3-6.el5.centos.1
setuptool-1.19.2-1.el5.centos
centos-release-notes-5.0.0-2
gzip-1.3.5-9.el5.centos
centos-release-5-0.0.el5.centos.2
httpd-manual-2.2.3-6.el5.centos.1
yum-3.0.5-1.el5.centos.2

Says what's installed.

[root@rubyplus ~]# cat /etc/issue
CentOS release 5 (Final)
Kernel \r on an \m

This is clear.