YUM: Error: Cannot retrieve repository metadata (repomd.xml) for repository

Screwed up your yum? Here is a quick way to fix by cleaning it up:

View repolist:
yum repolist all

Clean cached package downloads/headers:
yum clean all

Disable a repo temporarily:
yum --disablerepo epel install htop

Disable a repo permanently:
Remove or comment it out in: /etc/yum.repos.d/

More info:
http://docs.oracle.com/cd/E37670_01/E37355/html/ol_creating_yum_repo.html
http://www.tecmint.com/20-linux-yum-yellowdog-updater-modified-commands-for-package-mangement/
http://forums.fedoraforum.org/showthread.php?t=223472
https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/sec-Managing_Yum_Repositories.html
http://www.centos.org/docs/5/html/yum/sn-yum-maintenance.html