Recently CentOS commercial support is available for the distribution via OpenLogic. Centos previously did not not offer commercial support since it is a community maintained open source product. There are now a growing number of third party companies that will provide support for a price. Centos is maintained by a group of developers that regularly release updated versions of the distribution. It offers updates via public yum repositories but has no centos commercial support options available. Updates can be available for a few years which is generally the lifespan of a release of a distribution. Typically, Red Hat works off subscriptions. Centos requires no subscription. To update or upgrade your system use the yum package manager provided. For specific support questions one can always post in their forum or ask fellow administrators how to accomplish specific tasks. Mailing lists maintained by Centos is also a good support option, as opposed to other forms of more costly commercial maintenance.
Centos is free, and well put together. It is definitely recommended as an alternate to other commercial distributions.