The '--showduplicates' option for yum is useful for showing multiple versions of a package. I find it very useful when you have a very specific dependency and you are trying to find the specific name of a package to install. Imagine that you require a specific version of the pcre library for PHP.

yum search --showduplicates pcre

pcre-7.8-6.el6.i686 : Perl-compatible regular expression library
pcre-7.8-6.el6.x86_64 : Perl-compatible regular expression library
pcre-7.8-6.el6.x86_64 : Perl-compatible regular expression library

The output provides several versions of the pcre package, allowing you to select the desired version to install.