Very interesting command that shows you which package a specific command belongs to.
Example (checking the ssh command):
rpm -qif `which ssh`
Name : openssh-clients Relocations: (not relocatable)
Version : 5.3p1 Vendor: CentOS
Release : 84.1.el6 Build Date: Fri Feb 22 04:51:49 2013
Install Date: Wed May 22 02:30:06 2013 Build Host: c6b9.bsys.dev.centos.org
Group : Applications/Internet Source RPM: openssh-5.3p1-84.1.el6.src.rpm
Size : 1049931 License: BSD
Signature : RSA/SHA1, Sat Feb 23 18:42:22 2013, Key ID 0946fca2c105b9de
Packager : CentOS BuildSystem <http://bugs.centos.org>
URL : http://www.openssh.com/portable.html
Summary : An open source SSH client applications