The Epel respository offers CentOS and RHEL the ability to you the Fedora Extra Packages for Enterprise Linux, which includes many useful packages such as HAProxy and others.
Run the following as root or with sudo:
yum -y install epel-release
Sometimes you may not be able to install with yum, in that case you can install with RPM instead.
wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-5.noarch.rpm rpm -Uvh epel-release-5*.rpm
wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm rpm -Uvh epel-release-6*.rpm
wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm rpm -Uvh epel-release-7*.rpm