RPMs on the web:
http://www.rpmfind.net
http://rpm.pbone.net/

Installing:

rpm –ivh (name)

Listing Installed Packages:

rpm –qa | grep (name) to find installed packages

Removing Packages:

rpm –e (name)

Freshen packages:

rpm –F *.rpm

Building RPM from source:
http://wiki.centos.org/HowTos/RebuildSRPM

Find out what library is provided by an RPM package:

locate libg2c.so|xargs rpm -qf | sort | uniq

Multiple packages error:
Substitute the "zlib-devel" in the below to another package reporting duplicates.

rpm -qa --queryformat "%{name}.%{arch}\n" zlib-devel