The Remi Repo is a yum repository maintained by a French dude - Remi Collet. It contains much more up to date packages (January 2012) such as MySQL 5.5 and PHP 5.3.
Heres how I installed it on CentOS.
su -
cd/etc/yum.repos.d
wget http://rpms.famillecollet.com/enterprise/remi.repo
This file provides configuration for remi and remi-test repositories.
Note: The repository is not enabled on install (enabled=0). You need to enable it when you need it, for example :
yum --enablerepo=remi install mysql-server
or edit /etc/yum.repos.d/remi.repo and change enabled=0 to enabled=1 to enable it permanently.