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:
name=Dag APT Repository
[atrpms-stable] #I suppose all the atrpm repos will work, but this is only one I use.
name=ATrpms for Fedora Core $releasever stable