htop together with vim are the first things I install in a new Linux installation.
I usually do not use any RedHat or rpm distribution, but sometimes I have to deal with them, so when I am in front of a CentOS server the first thing I do is to install htop.
This is the best way I have found to do it, without touching the system too much.
Go to this page and download the latest version of htop. Be sure to download the correct version for your architecture. 32 or 64 bits.
Then install it using
rpm -i. Something like this:
rpm -i htop-1.0.2-1.el6.rf.x86_64.rpm
Now you can work on the CentOS server having htop tool.