Like many others I had the "no more mirrors to try" problem. About two
weeks ago everything was working fine and then yum updates started
failing yesterday 2006/05/04. Googling, I discovered many others have
the same problem, so here's how I got my YUM and YUMex working again
for FC4.

Following instructions from http://www.fedorafaq.org/fc4/ (unofficial
FC FAQ)...
Switch to root.
su -
Backup and update yum.
cd /etc
mv -f yum.conf yum.conf.bak
wget http://www.fedorafaq.org/fc4/samples/yum.conf
rpm -Uvh http://www.fedorafaq.org/fc4/yum

Some other information.. It says that yum.conf was updated 2005/07/29
so that file probably is not relavent, but the RPM for yum was updated
2006/02/03. I'm pretty sure that I had the update but my problem went
away afterward. Here's the output from the rpm command.

# rpm -Uvh http://www.fedorafaq.org/fc4/yum
Retrieving http://www.fedorafaq.org/fc4/yum
Preparing...
########################################### [100%]
1:yum-fedorafaq warning: /etc/yum.repos.d/dag.repo saved
as /etc/yum.repos.d/dag.repo.rpmorigwarning:
/etc/yum.repos.d/freshrpms.repo saved as
/etc/yum.repos.d/freshrpms.repo.rpmorig
########################################### [100%]

It looks like the update might have fixed dag.repo and freshrpms.repo
for me in addition to updating yum itself. Hope this will help others.