So, let's get this Linux train rolling!
 
Just putting out a list of RHEL/CentOS repositories that I use on all my servers. Mainly for the fun of it but mostly for the functionality of newer updates on the production servers I have. I'll try to explain which repository contains what but I may miss a few items. As with anything, please take this list not as 'required' but just something I functionally use quite often. Mileage will vary according to preferences/requirements for each system involved. Unless otherwise noted they will support any current version of RHEL/CentOS (5-7). That being said, here they are, in no particular order with relevant hyperlinks:
 
EPEL (Extra Packages for Enterprise Linux)
ELRepo (Hardware and Kernel updates)
REMI Repository (Latest PHP and a few backports)
Webtatic Repository (Updated Web-related packages)
 
And lastly a VMWare related repository which would need to be created manually. This is only necessary if you're running a virtual machine with RHEL/CentOS on ESXi hosts. The following procedure will get this repository available and active:
 
In the directory /etc/yum.repos.d, create the file (with your preferred editor, mine is vi) vmware.repo. Within that file you'll need to insert the following:
 

[vmware-tools]
name=VMware Tools for Red Hat Enterprise Linux $releasever – $basearch
baseurl=http://packages.vmware.com/tools/esx/latest/rhel6/$basearch
enabled=1
gpgcheck=1
gpgkey=http://packages.vmware.com/tools/keys/VMWARE-PACKAGING-GPG-RSA-KEY.pub

 
Once that is done you can implement all the necessary vmware daemons by issuing the following command:
 

$sudo yum install vmware-tools-esx-nox

 
If you are using the vmxnet3 virtual NICs on your VMs then you'll want to also add the common optimized drivers as well by issuing the following command:
 

$sudo yum install vmware-tools-vmxnet3-common

 
Let me know if you have any repos that you prefer.

RachelSkates
YUM is an command-line package-management utility for RPM based Linux systems, It has been released under the GNU General Public License. Yum is useful for rpms which have dependencies, Yum searches for all dependencies of any RPM in all available repositories.
Below list contains top 5 yum repositories (RPMForge, EPEL, REMI, ATrpms, Webtatic) for RHEL based systems with installation links, which we needs to keep our system up to date with latest packages. These repositories having most of rpms required for servers.
 
 

ATrpms has been depreciated and is no longer recommended as a valid repository. Considering it's not been updated in quite a long time I have removed it from my overall list of valid repos on my servers. The last update for ATrpms is 2014 of which a repo for Fedora 20 was updated. Nothing since then.