There are more repos. you can add but not necessarily a good idea as I believe reddazz mentioned in another thread that the possibility of package conflicts grow with too many repos. I've seen many of these conflicts as I have atrpms, freshrpms, and livna over the three Fedora repos, but I also have no problem working the conflicts out. Also, the more repos. the longer it takes for yum to pull up a list of packages when you are looking for updates or available packages. Here is a link to a good reference site for Fedora Core 6:
http://www.mjmwired.net/resources/mjm-fedora-fc6.html