I've been having the same problems. It looks like there was a change in the recent version of yum, and either some of the repositiories haven't been upgraded to fit the new format, and/or the url used in the yum.conf file needs to be changed.
I'm going to do a little more research into it today, if I find anything, I'll tell you, but in addition to the regular fe0dora repositories, here's the only one's I've been able to get to work so far:
[freshrpms]
name=FreshRPMs
baseurl=http://ayo.freshrpms.net/fedora/linux/$releasever/$basearch/freshrpms/
http://ftp.us2.freshrpms.net/linux/f.../fedora/linux/$releasever/$basearch/freshrpms/
[dag]
name=Dag APT Repository
baseurl=http://dag.freshrpms.net/fedora/$releasever/en/$basearch/dag
http://dag.atrpms.net/fedora/$releasever/en/$basearch/dag/
http://ftp.heanet.ie/pub/freshrpms/pub/dag/fedora/$releasever/en/$basearch/dag
[newrpms]
name=NewRPMs
baseurl=http://newrpms.sunsite.dk/apt/redhat/en/$basearch/fc$releasever
http://newrpms.atrpms.net/apt/redhat/en/$basearch/fc$releasever
[atrpms-stable] #I suppose all the atrpm repos will work, but this is only one I use.
name=ATrpms for Fedora Core $releasever stable
baseurl=http://apt.atrpms.net/fedora/$releasever/en/$basearch/at-stable
http://ftp-stud.fht-esslingen.de/atr...ms.net/fedora/$releasever/en/$basearch/at-stable
http://wftp.tu-chemnitz.de/pub/linux/ATrpms/fedora/$releasever/en/$basearch/at-stable